Crime Scene Training

Investigating Indoor Marijuana Grows

This video is made available by the Police Officer's Safety Association.

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Crime Scenes and Alternate Light Sources

By: Don Penven

Alternate light sources, a much needed tool for CSIs

Over many decades, visible light sources were used during most searches of crime scenes. Although some forensic investigators would occasionally use ultraviolet (UV Black Light) to examine for crime scene evidence, white light was the mainstay. But in the 1970s the Royal Canadian Mounted Police (RCMP) added a new dimension to forensic examination of physical evidence.

The “Mounties” pioneered the use of argon-ion lasers, but these expensive, cumbersome, bulky machines were impractical for use at crime scenes, so their use was limited to the crime lab.

The birth of alternate light sources

Portable lasers began to appear in the marketplace in the 1980s, but their usefulness was limited to mostly a single color of light. In the 1990s the availability of high intensity incandescent lamps slowly revolutionized alternate light source analysis of physical evidence since these machines, many weighing less than 20 pounds, could provide an intense light beam that could be passed through various filters covering from visible blue, green, yellow and red light. Using these colors enhanced the ability to reveal an abundance of what would otherwise be invisible evidence. But one element is still missing.

What is fluorescence?

Merely shining a blue or other visible color light onto an object in and of itself does not show us much. You see, certain materials possess a property called fluorescence. Fluorescence occurs when light of a certain color and light frequency strikes an object, and the object returns light of a different color and frequency. This fluorescence is much weaker in intensity than the light beam that created it, so to visualize the fluorescence, the crime scene technician must use filtration that blocks the visible light but passes the fluorescence. For example: if the visible light beam is blue light, the filter must be orange in color. This blocks the intense blue light but passes the weak fluorescence. UV light, on the other hand, is invisible, but it produces visible fluorescence from certain objects and substances. No filtration is required to view UV fluorescence, but eye protection in the form of clear glass or plastic lenses is recommended.

Detecting hidden blood stains in crime scenes

If you watch many of the TV “Cop” shows, you will see at some point those working a crime scene using a blue light in search of invisible blood (blood stains that were cleaned up). Shazam! Blue-white stains appear all over the floors, walls and objects sitting around the crime scene! But in reality—this cannot happen. You see, blood does not fluoresce by applying UV or visible blue light.

Blood, even minute quantities that remain after clean-up, can be made to “luminesce; that is, by spraying certain chemicals such as Luminol, BlueStar or Fluorescene on the various surfaces, blood will luminesce, or simply “glow in the dark”—and adding blue light is not necessary. So what can alternate light sources reveal? Although blood does not fluoresce, certain other physiological fluids will. UV alternate light sources can reveal the following: seminal fluid, saliva and urine stains. Also, certain narcotics will fluoresce as will bone and teeth fragments.

Other uses of alternate light sources Indeed, many forms of physical evidence will fluoresce. But modern science has resulted in the development of chemicals that “make” objects fluoresce. When using fluorescent chemicals, latent fingerprint development can be greatly improved. Fluorescent latent print powders have the ability to make the latent residue on a surface fluoresce. The benefit here is that the ridges fluoresce brightly and when photographed, a multi-colored or confused background can be minimized to the point where it does not show up in photographs. Fluorescent liquids are used to develop latent prints on porous surfaces such as paper and cardboard.

Fluorescent dyes are used to enhance latent prints developed using superglue fuming. The use of alternate light sources provides a highly practical and efficient means of locating physical evidence at crime scenes. The invention and perfection of Light Emitting Diodes (LEDs) has further advanced evidence recovery since even 1 and 3 watt LEDs can be installed in small, hand-held flashlights, and their performance is remarkable.

To learn more about the methods and tools used by today’s real-world crime scene investigators, please check out the Categories in the navigation window to the right. 

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To check out various alternate light sources, download the Introduction to Alternate Light Sources

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How police tracked down Steve Jobs' stolen iPads

Digital breadcrumbs left by the iMac and iPad computers were key in tracking them down

 By Martyn Williams

IDG News Service - The digital breadcrumbs left behind when people use Internet-connected gadgets are what led California investigators to recover iMacs, iPads and other items stolen from the home of the late Apple CEO Steve Jobs.

 Based on the police report, obtained by the IDG News Service, here's how they did it.

 The burglary took place while the Jobs family home, in a leafy and quiet area of Palo Alto, was being renovated and was unoccupied. Sometime between the construction crew leaving the site at 5:00 p.m. on Tuesday, July 17, and arriving just before 8:00 a.m. the next morning, someone entered the house and stole several personal effects and Apple gadgets.

 Within several days, the Palo Alto Police Department had enlisted the help of the Rapid Enforcement Allied Computer Team, a San Jose-based organization formed by local, state and federal law enforcement agencies that specializes in computer-related crimes. Local police wanted assistance tracking down the Apple computers and iPads that were reported stolen from the house.

 The REACT team reached out to Apple's own investigators, who had access to the company's computer systems, and supplied them with a list of serial numbers of stolen devices. Apple was quickly able to determine that one of the stolen iPads had connected with Apple's servers soon after the burglary.

 The iPad was trying to reinstall its operating system and was recorded connecting from an AT&T U-verse Internet IP address from 7:22 a.m. to 7:31 a.m. on July 18, the morning after the house was broken into and minutes before the returning construction workers would discover the break-in.

 Upon searching logs for the IP address, Apple investigators discovered a different iPad had connected from the same address at 8:10 a.m. on July 17, before the burglary took place, and again at 1:56 p.m. on July 20, after the break-in was reported to police. That iPad wasn't suspected stolen, but the iTunes account information gave investigators a lead.

 Tied with information from AT&T U-verse about the Internet connection, investigators were led to an address in Alameda, on the east side of San Francisco Bay. At that address Kariem McFarlin, the suspect in the case, was paying for AT&T Internet service, according to investigators.

 While police were building their case there was more activity on the stolen devices.

 Over a five day period, Apple investigators recorded activity on McFarlin's iTunes account linked to the iPad that originally connected to restore its operating system, a second iPad stolen from the Jobs' home and an iMac computer that was also missing, according to police. One of the iPads later connected from a Comcast Internet connection in Alameda using a different iTunes account.

 Investigators say they searched McFarlin's Facebook page and discovered their suspect and the owner of this new iTunes account were friends.

 Before investigators made their move there was one final check that had to be made.

 They traveled to the Alameda address where McFarlin lived and swept the immediate area for Wi-Fi signals.

 Police wanted to determine whether there was an open Wi-Fi network that perhaps was being used without the owners' permission. If the AT&T Internet address was tied to an unsecured connection, it could complicate the case because anyone could have used it. Finding only secured Wi-Fi signals, investigators could argue it was being used by the person paying the bill or those with permission.

On August 2 police entered McFarlin's apartment and discovered one of the stolen iMac computers on his kitchen table, according to the police report.

 The other iPads were recovered from people associated with McFarlin, the police say.

 To get rid of stolen jewelry, McFarlin told police, he had Googled selling jewelry and found a dealer in Pennsylvania. Police say they found email messages in McFarlin's phone indicating the sale and were able to recover the stolen jewelry by contacting the broker.

 In a subsequent interview with McFarlin, police say he admitted breaking into the home by climbing over the builders' scaffolding and finding a spare key for the house in the garage. He said he stole two iMacs, three iPads, three iPods, one Apple TV, a diamond necklace and earrings, and several other items.

 In explaining his actions, investigators say McFarlin said he had money problems and had taken to breaking into houses. He wrote a single page letter of apology admitting he had burglarized Steve Jobs' house and stolen property, but had done so because he was desperate.

 McFarlin is due in court on Monday.

 Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service.

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BloodTips-04 Hemastix Blood Test Strips

By Don Penven

Chemical field testing for blood using “presumptive" methods has long been practiced by crime scene investigators. Granted, many of the red to reddish brown stains found at crimes scenes are “obviously blood,” and presumptive testing may be eliminated. This circumstances may be when the victim is lying in the middle of a large red stain.

But when it comes to possible blood spatter in various areas of the crime scene, a chemical field test is in order.

As with any chemical field test, avoiding contamination to the suspected stain is mandatory. Thus, the contact method is used to lift a sample of the stain while leaving it intact and uncontaminated. This is easily accomplished by moistening a piece of clean filter paper or cotton-tipped swab with distilled water. All tests are ten performed on the lifted stain.

Hemastix® are 3” plastic strips with a special blood reagent material at the tip. The strips detect the peroxide-like activity of hemoglobin in a substance. Simply rub the Hemastix on a moistened stain as collected above or across a swab that has a suspected dried blood sample on it. The reagent coated tip will turn a shade of green if hemoglobin is detected. Compare the color reaction to the chart on the side of the bottle to determine the level of hemoglobin in the sample. If the reaction is positive, take a photograph of the test strip by the substance to document the reaction and retain the strip as evidence.

Please note: Expired Hemastix®  will generally still react to the presence of blood, but should only be used for training purposes. Also, Hemastix®  will not detect the difference between human and animal blood.

Hemastix Blood Test Strips

RUVIS and The Effects of Ultraviolet Light Exposure on DNA Analysis of Fingerprints

Julie Luby Nicholson*, M.F.S.; Todd W. Bille*, M.S.; Michael J. Malia*, Ph.D; Robert A.

Bever*, Ph.D. 

 

 

 

The Sirchie® KRIMESITE Imager. is a tool that can be used to detect and document latent fingerprints on various surfaces without the use of chemical enhancement. The Imager takes advantage of the different UV light reflectance properties of the fingerprint and the surface on which it is located. Large surfaces can be searched quickly and then any fingerprints detected can be digitally photographed for comparison purposes. Due to the use of specific optic filters, the search for fingerprints can be conducted in daylight or darkness. A growing trend in forensic DNA analysis is the analysis of the epithelial cells contained within a fingerprint or fingerprint smudge that is not suitable for fingerprint comparison purposes. One concern from a DNA analysis perspective is the exposure of the limited biological material to the UV light used by the KRIMESITE Imager. which can be harmful to the DNA. 

The objective of this study was to determine the effects of ultraviolet light on DNA analysis and to determine the ideal circumstances for biological fluid examination when using a shortwave ultraviolet light source. 

Human buccal cells on paper were used to simulate a biological stain. The cells were exposed to a 12 Watt, shortwave (254nm) ultraviolet light for one minute, two minutes or three minutes at distances of one foot, two feet, or three feet. After exposure to the ultraviolet light, DNA was extracted from the stains for subsequent quantification and STR (Short Tandem Repeat) analysis using PowerPlex® 16 (Promega Corporation). 

Results indicate that short-term (one minute) exposure of these biological samples to ultravioletlight does not greatly affect downstream DNA analysis. A longer exposure (two minutes) at a short distance (one foot) causes allelic dropout, which may be due to degradation of the biological sample. However, increasing the exposure distance to two feet or three feet improves the recovery of DNA from the paper. DNA analysis was most affected by longer exposure (three minutes) to ultraviolet light, resulting in poor recovery and increased allelic drop out.

 This technique was subsequently used on probative evidence successfully. Ultimately, this information will be applied to the examination of fingerprints and a method will be developed to scan evidence for biological stains using ultraviolet light causing minimal damage to the DNA.

 *The Bode Technology Group, Springfield, Virginia

 

RUVIS Photo of

latent Print on Soda Can

BloodTips-03 Luminol Reagent

By: Don Penven

Luminol is a chemiluminescent substance that is used as a presumptive test for the presence of blood. Making use of the peroxidase-like activity of the heme portion of hemoglobin, Luminol produces a bluish-white light that can be viewed in total darkness. Invisible blood stains react with the Luminol reagent by luminescing—but darkness is essential. Luminol is a useful test for searching large areas for blood, especially if the area has been cleaned up. Sensitivity:1:100,000.

 

Luminol is available in several different packages and quantities. It is supplied as a pre-measured dry powder along with a specific amount of distilled water. Once mixed, Luminol has a relatively short shelf life.

The advantages of using Luminol for locating minute traces of blood are numerous: it is non-destructive to subsequent DNA profiling; it is a relatively safe compound if used according to directions; and it is simple to mix and apply.

 

Preparations for use:

Note: Since the luminescence fades rather quickly, have a tripod-mounted camera ready to use as soon as luminescence appears.

Warning! Luminol, in its solid or mixed state, is hazardous and should be mixed in a well-ventilated area or laboratory hood. Severe skin, eye and respiratory irritant—wear protective clothing, gloves and safety glasses/goggles.

1. Remove cap from bottle of “B” solution.

2. Remove clip and pour entire contents of pouch “A” powder into bottle of “B” solution.

3. Recap bottle with supplied spray head attachment and shake well until all solid material dissolves.

4. Luminol is ready to be applied to suspect areas. Set the spray nozzle to “MIST.”

Instructions for use:

1. Photograph the scene prior to processing with Luminol.

2. Turn off all lights and darken the area as much as possible—luminescence may be very weak and is best seen in total darkness. Note: A night vision flashlight (red beam) such as LVL100 LumaVision™ may be used to illuminate the area while processing the scene.

3. Process small 2-3 sq. ft. areas at a time. When luminescence is revealed, prepare to take photos  (absolutely no flash is to be used). Notes: Photo Evidence Markers such as PEN15 can be used to indicate the locations of luminescence so they can later be photographed under full light or with a flash.

4. Reapply Luminol as necessary if luminescence fades too quickly before photos can be taken.

 

 Carpet suspected of holding blood prints

 

 

 

 

 

 

 

 

 Luminol developed footprint

 

 

 

For complete instructions, you may download the Technical Information Bulletin on Luminol 

 

BloodTips-02 Dischaps Reagents

By: Don Penven

Note: Dischaps is the name of a product line manufactured by Sirchie Finger Print Laboratories. It refers to the type of packaging for a series of different chemical reagents. This packaging refers to DISsposable CHemical Applicators.

 

DISCHAPS™ packaging virtually eliminates the possibility of contamination of chemical reagents, and it dramatically increases shelf life. Reagents are contained within easily crushed glass ampoules. The ampoules are then sealed inside tough, flexible polyethylene dispenser tubes.

Blood DISCHAPS™ applications rely on using the contact method of testing—that is, a few drops of ethyl alcohol or distilled water (See Technical Information Bulletin) are placed on a strip of filter paper, and the wet filter paper is pressed against the suspected stain. The DISCHAPS™ reagent is then applied to the filter paper, thus preserving the original evidence stain.

 

PHENOLPHTHALEIN DISCHAPS™ (DCB100)

Note:  Phenolphthalein reagent requires that ethyl alcohol be used to wet the filter paper during the contact stain lifting method.

Blood causes a Pink stain in just a few seconds. This reagent is considered by many field crime scene technicians to be one of the most reliable presumptive tests for the presence of blood because of its non-reaction to plant materials. Sensitivity=1:500,000.

 

Phenolphthalein reagent reaction to blood 

 

 

LEUCO-MALACHITE DISCHAPS™ (DCB200)

An intense Blue/Green color reaction in 3 seconds is presumptive evidence that

blood is present. Sensitivity (1:10,000).

 

Leuco-malachite Reaction

 

 

LUMINOL DISCHAPS™ (DCB300)

 Luminol reagent requires a darkened area for observation. This is the ideal reagent for

“aged” or invisible blood stains. In fact, the older the stain, the brighter the Blue/

White color reaction (within five seconds). Sensitivity: 1:100,000.

 

Luminol Reaction

 

 

For more specific instructions for use of the Dischaps Blood Test Reagents, you may download the Technical Information Bulletin  <===

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BloodTips-01 Introduction to On-Scene Identification of Blood

By: Don Penven

The purpose of BloodTips is to provide quick tutorials in the use of the most frequently used blood screening methods at crime scenes. These tests are PRESUMPTIVE in nature. They, like narcotic and drug field tests, serve a singular purpose—they provide the crime scene investigator with the knowledge that a particular stain possesses the possibility that it is blood, and these tests are not a substitute for crime laboratory analysis.

The most commonly employed field tests available for use at crime scenes are:

1. Phenolphthalein
2. Leuco malachite
3. Luminol

A variety of commercially-available packaging methods permit simplified, uncomplicated use of these reagents at crime scenes. Each BloodTips post will present a simplified application procedure while existing posts on this blog provide more in-depth coverage of these techniques.

Uses are strongly advised the conduct their own experiments using each of these processes prior to any use at a crime scene. The crime scene investigator is also encouraged to examine the Material Safety Data Sheets (MSDS) readily available from the manufacturer to learn of any hazards that may exist when using these reagents:

To download these MSDSs, please use the following links:

Phenolphthalein:  Download DCB100A   Download DCB100B

Leuco Malachite:   Download DCB200A   Download DCB200B

Luminol:   Download DCB300

 

 The Contact Method of Testing

In order to preserve the integrity of the stain to be testing, we strongly recommend that the Contact method of stain sampling be used in all cases.

Procedure:

• Using a clean piece of filter paper, moisten it by adding a few drops of ethyl alcohol or distilled water, whichever is indicated on the instructions accompanying the particular reagent.
• Press the wet filter paper against the suspected stain for a few seconds.
• Please the filter paper test strip on a clean surface (paper towel, napkin, etc.)
• Add the test reagent to the stain.

In the case of phenolphthalein a pink stain will develop in a few seconds indicating the presumptive presence of blood.

In the case of leuco malachite an intense blue/green stain will develop in a few seconds indication the presumptive presence of blood.

In the case of luminol, the presumptive presence of blood will be indicated to a bluish-white luminescence.  This luminescence is only visible in near total darkness.

 

Check out BloodTips02

 

Was Sherlock Holmes The First of a Long Line of Crime Scene Investigators

By: Don Penven

The adventures of Sherlock Holmes began in 1887 with the publication of A Study in Scarlet, the
first of four novels and 56 short stories penned by British author, Sir Arthur Conan Doyle. Few fictional characters have survived the test of time, but Holmes continues to thrill, and yet befuddled many readers to this day. Motion pictures and TV documentaries keep the legend alive.

Holmes and Watson—a Dynamic Duo

 The exploits of Holmes, and his roommate and biographer, Dr. John H, Watson, have fascinated countless generations of crime fans eager to learn more about this London-based "consulting detective," whose uncanny abilities defy normal thought-processes of most Holmes devotees. Through skillful narration, using the words of Holmes, Watson and also third-person script, Conan Doyle mesmerized his followers with Holmes’ use of logical reasoning, the ability to devise virtually any form of disguise, all coupled with an in-depth knowledge of forensic science.

Author Conan Doyle stated that the inspiration for Homes was the persona of Dr. Joseph Bell, for whom he clerked at the Edinburgh Royal Infirmary. He also admitted to using snippets from lecturer, Sir Henry Littlejohn.

Keeping Track of the Criminal Population

 A system of criminal identification was implemented in Europe prior to Conan Doyle’s introduction of his master detective. Alphonse Bertillon. a French anthropologist, introduced his system of anthropometry, a method requiring precise measurements of the bone structures of incarcerated criminals. Bertillon’s formula of measurements was used to verify the re-arrest of the criminal element. It was not until 1903, as a result of the Will West case (more on this at the website listed below) that anthropometry was shelved to make room for the new science of fingerprint identification.

The Introduction of Fingerprint Science

During this same fateful year when fingerprint identification was heralded as a new science, Conan Doyle published the Adventures of the Norwood Builder, in which a bloody fingerprint provides a solid clue to the nature of the crime in question.

Fingerprint identification reigns-supreme as a virtually infallible means of identification. But some forensic specialists would challenge this determination, countering that DNA profiling is a far more accurate means of identifying a perpetrator. No doubt this debate will rage on for some time to come.

The CSI Phenomenon

Once of the most successful television dramas of the past decade is “CSI: Crime Scene Investigation.”  Along with its progeny, CSI Miami and CSI New York, this series has done more to influence how crimes are solved than all of the textbooks on the subject combined.  Unlike so many “cop shows,” the CSI-series has created a new public awareness—to the point that many affected crime victims expect their particular brush with the criminal element  to be solved within an hour (less the time for commercials), using futuristic methods and crime scene equipment . The CSI characters utilize the most innovative forensic examination equipment and work in pristine, shiny new laboratories equipped with every conceivable evidence discovery, evaluation and identification tool imaginable. But just taking into account the economic stress most crime labs are feeling, cost often outweighs practicality.

Now doubt, most people would agree that Sherlock Holmes was the ultimate model for today’s CSIs, even if they never read a single one of Conan Doyle’s novels or short stories. The very name serves as a monument to the fictional character that frequently set forth from his lodgings at 221b Baker Street to pursue evil-doers wherever their crimes may have occurred.

This website is devoted to providing information covering the various disciplines of crime scene investigation, The list of Categories in the right navigation window will provide the reader with time-tested methods and applications for the myriad situations the crime scene technician will face at the scenes of crimes. 

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Watch the PSA - Slow Down or Move Over 

 

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Overview of Chemical Tools and Methods for Latent Print Development

Powders

Powders adhere to both water and fatty deposits. These are generally useful

on newer prints only. Choose a powder to contrast with the background. They

are useful on any dry, relatively smooth, non-adhesive surfaces. Use after

laser fluorescence. May be used before ninhydrin and after cyanoacrylate.

Results may vary with skill of technician. “Lift” developed prints by

photography or conventional methods.

Fluorescent Powders

Powders made of fluorescent materials offer advantages to the limitations of

conventional powders. Apply as with conventional powders. “Lifts” can be

made photographically or by conventional means. Fluorescent powders are

especially useful on confused backgrounds. An ultraviolet or forensic light

source is required.

Iodine Fuming

Iodine fumes react with oils and fatty deposits to produce a temporary

yellow-brown reaction product. Iodine is useful on fresh prints on porous

and non-porous, non-metallic surfaces. Developed prints must be fixed or

photographed immediately because reaction will rapidly fade. Use iodine

before ninhydrin and silver nitrate.

DFO

DFO, 1,8 Diazafluoren-9-one, is a fluorescing ninhydrin analog found to

develop up to two and a half more prints than ninhydrin itself. It is useful on

porous surfaces, especially paper. Development may be accelerated through

the application of controlled heat. Use it before ninhydrin. DFO also is useful

to develop weak blood stains. It requires a specialized light source, such as

the BLUEMAXX™.

Ninhydrin

Ninhydrin reacts with amino acids to produce a purple reaction product

called “Rhuemann’s Purple”. It is useful on porous surfaces—especially paper.

Development time is up to 10 days, but may be accelerated through the

application of heat and humidity. Use ninhydrin after iodine and before silver

nitrate. Ninhydrin is not useful on items which have been exposed to water.

Silver Nitrate

Silver nitrate reacts with the chlorides in skin secretions to form silver

chloride, a material which turns gray when exposed to light. Developed prints

must be photographed immediately because the reaction will eventually (and

permanently) fill the background. It is useful on paper, cardboard, plastics and

unvarnished, light-colored woods. Use it after ninhydrin and iodine. It is not

useful on items which have been exposed to water.

Physical Developer

Physical developer is another silver-based developer which reacts to form a

dark gray reaction product. It is useful on paper, cardboard, and unvarnished,

light-colored woods. Use physical developer after ninhydrin and iodine. It is

very successful on items exposed to water.

Cyanoacrylate (Glue Fuming)

Cyanoacrylate fumes react (polymerize) with water and other possible

fingerprint constituents to form a hard, whitish deposit. It is useful on most

non-porous and some porous surfaces. Cyanoacrylate produces excellent

results on styrofoam and plastic bags. Developed prints may be dusted with

powders or treated with fluorescing dyes, such as ardrox and basic yellow to

enhance.

Amido Black

Amido black reacts with the proteins found in blood to form a black reaction

product. Amido black is useful only on blood-contaminated prints. It is highly

sensitive. It is useful on non-porous and some slightly porous surfaces. It

sometimes offers successful development of blood prints on dead human

skin

Adhesive Side Powder

Adhesive side powder attaches itself to plastic print impressions on the

adhesive side of tapes. It produces excellent results on light-colored or

transparent tapes, including duct tape, masking tape, plastic surgical tape,

foam tape, clear and reinforced packing tapes and labels. This process

involves wetting tapes.

Fluorochromes

Prints may be treated with special dyes called fluorochromes which easily

are made to fluoresce and bond with the print deposits. They are useful

with forensic lights such as SIRCHIE’s BLUEMAXX™. DFO is a fluorescing

ninhydrin analog found to develop up to two and a half times more prints

than ninhydrin itself. It is useful on porous surfaces. Development may be

accelerated through the application of controlled heat. A specialized light

source such as  SIRCHIE’s BLUEMAXX™ is required. Basic yellow, ardrox, and

rhodamine are dyes especially useful staining latent prints developed with cyanoacrylate.

Download more information: Latent print Development

 

PrinTips 11—An Overview of Latent Print Development Powders

By: Don Penven, Tech Support

Latent print powders come in five different formulations:

Regular-Oxide, Metallic, Magnetic, Combination and Fluorescent. This article covers the basic theory of each type. Keep in mind that if you are uncertain which powder to use on a particular surface—experiment by placing your print in an area not likely to have been touched by the perpetrator.

 Regular-Oxide Powders

These powders are considered the basic choice by crime scene investigators for use on many of the surfaces encountered at crime scenes. But many practitioners are not aware of some of the limitations. Examples of regular-oxides are: black, white, gray and red. These finely milled powders are highly sensitive toward the moisture or oily content of latent fingerprints. But their use should be limited to just non-porous surfaces such as most painted metals, plastics, waxed surfaces, glass, rubber, leather  and wood (painted and unpainted). They should not be used on highly polished surfaces such as chrome or silver plating or other polished metals. Regular-oxide powders are applied with a brush. A powder color is selected based on how much contrast from the background it affords. Use black powder on light-colored surfaces and white powder on dark colored surfaces. Gray and red powders are often used on either light or dark surfaces.

 Metallic Powders

As the name suggests, these powders are formulated from metallic substances such as aluminum, copper and zinc. They are specifically formulated for use on highly polished surfaces like chrome or silver plating. Using a regular-oxide powder on this type of surface generally results in the moisture residue from latent prints being damaged or destroyed—these ridge structures are simply wiped away. Metallic powders are applied with a brush.

 Magnetic Powders

Magnetic powders are formulated from iron or iron oxide. The powders themselves are not magnetic, but they are easily magnetized by a magnetic wand. Magnetic powders may be used on virtually any surface EXCEPT a surface containing iron or steel. The principle of delivery is this: a magnetic wand is passed over the powder, which is then attracted to the wand to form a “brush” made of the powder. The CSI then passes this powder brush over the surface so that the tip of the wand does not touch the surface, but the powder does.  When carefully applied, magnetic powders leave very little surface residue so cleanup is simplified. Magnetic powders are available in black, gray and white for contrast with the surface.

 Combination Powders

These powders combine the properties and chemistry of both regular-oxide powders and metallic powders. The benefits here are:

1. Combination powders may be used on virtually ANY non-porous surface
2. These powders appear dark on a light background and light on a dark background.

Combination powders are applied with a brush.

 Fluorescent Powders

Note: fluorescent powders use a formulation similar to regular-oxide powders and are thus best suited to work on those surfaces mentioned above.

Fluorescent powders appeared in the crime scene kits of CSIs who wanted a powder that was usable on multi-colored, confused backgrounds like soda cans, snack wrappers and bags, wallpaper, ceramic surfaces, etc. These powders contain a chemical that produces fluorescence when exposed to ultraviolet (UV) light or certain frequencies from alternate light sources (blue, yellow, green and red). When developed latent prints are viewed under subdued ambient light the fluorescence is bright enough that when the prints are photographed, the background is mostly dropped out. Fluorescent powders are applied with a brush.

 For more information on latent print development using powders, chemicals and fuming techniques, download the Latent Print Development section of our catalog and read over pages 9-12.        Latent Print Development

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