Crime Scene Training

CasTips04 Tire and Footprint Casting Techniques

By: Don Penven

Two different materials have been popular for the collection of 3-D impressions in soil, sand and snow: plaster-of-paris (POP) and dental stone. POP was the medium of choice until sometime in the early 1990s. POP began to fall out of favor for several reasons; here are just a few:

1. Compared to dental stone, POP has a slight shrinkage factor. This drawback will be hardly noticeable in small casts—but it is a factor none the less.
2. Compared to dental stone, POP is far more brittle, and thus is easily damaged through handling of the casts.

POP remains popular as a casting medium because it is less expensive than dental stone. But because it is much more fragile—it becomes necessary to add reinforcement to the casts while the plaster is still wet, and you need to use nearly twice as much plaster to ensure a cast that won’t snap in half when you pick it up. So… is the cheaper price really worth it? From this point on, all directions will refer to dental stone (casting medium).

I first began hearing about dental stone as a casting medium way back in the early 1990s. I had contracted to teach an impression evidence seminar for a North Carolina law enforcement agency. At the time, the only source for this material was dental supply distributors. The product was used in dental labs.

So much for history…now let’s get to work at recovering tire and footprints impressions.

Advanced Preparation:  In advance of a casting assignment, make up several pre-measured Zip-Top bags of dental stone. Weigh out 2 lbs. of dental stone for each bag. When mixing you will need about 16 oz. of water per bag. This formula produces enough casting material to cover a 12-inch long impression.

STEP 1. Preparing the impression for casting:  Remove any debris ON TOP of the impression. Any objects (twigs, leaves, trash) embedded in the impression should be left alone.

STEP 2. Photograph the impression. Using a tripod, position the camera directly above the impression, at a right angle to the surface.

STEP 3. A minimum of four photos are taken of each impression: 1 – without a scale, 3 – with a scale

STEP 4. Using a flash attached to an extension cable, take three photos from the positions shown in the diagram below.

STEP 5. Prepare the impression for casting. Apply 3-4 coats of a clear lacquer (dust & dirt hardener) over the entire impression. Allow 2-3 minutes drying time between coats.  (Optional – If available, after the lacquer has dried, apply one thin coating of silicone spray release agent.)

Step 6. Place a casting frame around the impression. If the area to be cast is level, the frame may not be necessary. Using dental stone only requires that the cast be ½” to ¾” thick

STEP 7. Add 16 oz. of water to one of the 2 lb. bags of dental stone, zip it closed, and begin kneading (squeezing)  the bag to facilitate mixing the bag contents.  Keep working at removing any lumps of casting material.

STEP 8. Once a smooth mixture is apparent, open the bag and begin pouring the mixture onto the impression. Use a large spoon or similar item to break the fall of the casting material. Begin at one end on the impression and continuing pouring across the surface of the full impression, Use all of the casting material in the bag.

STEP 9. After about 15 minutes, lightly scratch identifying marks on the top surface of the cast. Setup time will vary upon the current humidity and temperature. When you cannot make an indentation in the surface of the cast with a fingernail, the cast may be carefully lifted from the surface (35-45 minutes setup time).

STEP 10. Invert the cast and set it aside to allow the bottom surface to dry.



Special Note: Most crime labs caution CSIs not to make any attempt to clean the dirt from the cast. Simply allow the cast to be fully dry—at least 6 to 8-hours, and then package it for delivery to the lab.

Special Note: This same procedure is used when casting tire impressions. Ideally you need to cast one full rotation of the tire. Just remember that one 2-lb. bag of dental stone will cover a 12-inch long footprint. Note: Casts should not exceed 20 to 24-inches in length.

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CasTips03 – Recovering Dust Impressions

By: Don Penven

Methods for Lifting Dust Print Impressions

Dust impressions are fragile at best, so the utmost care must be taken when attempting to lift them. Some methods work better than others, so it is suggested that you make several trial runs before going after the real thing.

1. Using adhesive materials to lift dust prints. Prior to the invention of the electrostatic dust print lifter, dust prints were recovered using adhesive-backed materials like tape.  Fingerprint lifting tape, especially the wide variety, does a fair job as a lifting medium. The widest latent lifting tape I am aware of is 4-inches. So it will be necessary to put down two lengths, side-by-side in order to retrieve a normal adult shoe print. If using 2-inch wide tape, use three or more strips.
   1. Use the tape in the same manner as when lifting latent fingerprints. Pull off a few inches of tape and tack down the end at one end or the other of the dust print to be lifted.
   2. Press the tape along its length to the surface using every effort avoid any air bubbles.  The tape should extend 2-3 inches beyond the beginning or end of the impression.  When the impression is covered, cut the tape with scissors and puck back about 1-inch (stick it to itself) because you are going to need something to grasp when you lift it from the surface.
   3. Add another length alongside of the tape on the surface and allow it to overlap the first tape by about 1/4 –inch along its length.
   4. Add a third and fourth strip if using a narrow tape (1.5 – 2-inches)
   5. You will need some form of backing material, preferably black in color, for mounting the tape. Most suppliers of fingerprint lifting tape also offer plastic backing materials.
   6. Slowly lift the tape(s) in one continuous motion.
   7. Attach one end of the tape(s) to the end of the backing material and slowly press it into place on the backer.
   8. The electrostatic dust print lifter eliminates the complications of the tape lifting process. A number of these devices have been available for several years. The one depicted here is unlike most competitive models since it does not require any wires or complicated hookup.
      1. Once the impression is located and photographed, a pickup mat is placed over the impression—black side down.
      2. The charging unit is positioned as shown below on the charging mat and metal ground plane
      3. When the charging unit is energized, it imparts an electrostatic charge to the surface, thus charging the dust particles present. These particles are then attracted to the charging mat.
      4. Turn off the charging unit and lift the mat from the surface. Note: Charging mats are supplied in 2’ x 3’ sheets, and they may be cut to smaller sizes when lifting a single dust print.
      5. The impression on the mat is photographed and then may be placed in storage/shipping boxes supplied by the manufacturer.

You may download the Technical Information Manual for the Electrostatic Dustprint Lifter HERE

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CasTips02 –Recording Dust Print Impressions

Crime Scene Investigation-- The Recording Dust Print Impressions

By: Don Penven 

Dust prints occur at crime scenes as a result of two influences:

1. They are tracked into a structure as a result of dust, dirt, pollen or other foreign material adhering to the soles of shoes
2. Once inside the subject may walk through a dust covered area and will leave negative impressions—where the existing dust was removed by the footwear and will leave positive impressions in areas where the transported dust is deposited on floors.

The search for dust impressions must begin prior to any other activity except for rendering aid to injured persons.

The Search for and Recording of Latent Dust Prints

The first challenge is to locate any possible dust print impressions.  The most effective method available is a flashlight. If possible, darken the room (total darkness usually is not necessary).

1. Direct the light beam across the floor at floor level. Dust impression, if present, will become immediately visible. 
2. Mark each visible impression with an evidence marker such as an evidence tent.
3. Once all available impressions are located and marked, photograph them as follows:
   1. Using a tripod, position the camera directly above each impression—at right angles to the surface.
   2. Always include a scale in each photo taken
   3. Assuming you are using a digital camera (and if not, why not) use the flashlight beam as a light source or use a flash that may be extended from the camera via a flash extension cable. The light (or flash) should be aimed at an oblique angle similar to what you used to originally locate the prints. The digital camera will provide an immediate preview of the impression.
   4. Maintain a written log of each photo taken.
   5. Be certain to pin-point the location of the impressions on the crime scene sketch. 

Special Note: If the crime scene is being recorded on video, be certain to get video footage of the location of the prints as well as close-up shots. While video isn’t very useful in the actual comparison of the dust prints with a suspect’s shoes, it will give the jury a glimpse of what you were working with. 

Once you are satisfied with the quality of your photos you may consider recovering the impressions if you are equipped to do so. The next article in this series, PrinTips03 – Recovering Dust Impressions, will cover several methods for dust print recovery. 

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CasTips01 – Introduction to Impression Evidence

By: Don Penven

An Introduction to Impression Evidence

It’s been more years than I can remember when I first heard the term “Moulage.” It was an old detective movie and one of the officers at a crime scene suggested making a moulage of footprints near a body. We certainly don’t hear this term used much anymore.

Moulage in French means “casting,” and today the term is used by some to describe a form of makeup used to simulate wounds on the body for EMT training purposes.

Casting is the accepted term used at crime scenes and it refers to making casts of 3-dimensional evidence like toolmarks, footprints and tire tracks. But I’m getting ahead of this story…

In his book, “Footwear…The Missed Evidence,” Dwayne S. Hilderbrand, M.Ed., states: In almost every criminal investigation it is necessary to determine and prove that a particular person or persons may or may not have been present at the scene of a crime. For this reason, the collection, preservation and analysis of physical evidence has become more frequent in the law enforcement community.

Around 1910, a criminologist by the name of Edmond Locard arrived at a theory that every time something comes into contact with another it either takes or leaves a portion of itself or another. This theory is called the Edmond Locard Theory, which simply states "Every contact leaves its trace." This theory is continually used today in crime scene investigations and the analysis of physical evidence.

Since criminals must enter and exit crime scene areas it should therefore, be reasonably assumed that they may leave traces of their footwear. Criminals have become smarter and wiser by beginning to frequently wear protection over their hands to avoid leaving fingerprints, and masks over their faces to avoid eyewitness identification. However, they are rarely aware of, or make little attempt to conceal footwear. During an every- day routine it is normal to see an individual wearing gloves, but it's not normal to see individuals wearing protection over their shoes.

The CasTips-series of articles on this blog is an attempt to bring more crime scene investigators under the awareness that impression evidence can serve as silent testimony in criminal cases, but the biggest problem is that all too often it is overlooked or accidentally damaged or destroyed.

Impression evidence can become apparent in two forms:

• 2-Dimensional: This type of evidence includes dust or dirt prints, blood prints (footwear and fingerprints) or shoe prints in some foreign substance such as oil or grease on a garage floor.
• 3-Dimensional:  This type is usually the most visible form of 3-D impressions that are left behind in soft or wet soil, sand and snow. Touching wet paint or soft foods like butter or cheese are forms of evidence left behind by the perpetrator.

The effectiveness of crime scene security often determines if impression evidence will be available. The most fragile form, the type most often overlooked or destroyed, is dust print evidence. This is due largely to the intrusion of the first responders including emergency medical as well as law enforcement personnel. What is often lacking is formal training and an awareness of the fact that dust impression are often found in the tidiest of structures, let alone some of the hovels you may encounter.

The initial officer on the scene is the key to impression evidence survival, and these individuals must be given the awareness of just how valuable impression evidence can be. Protecting the crime scene is vital, but all too often it becomes impractical when serious injuries of victims are apparent. Still, keep in mind that the perpetrator will most often follow a distinctive, direct course through a structure so it behooves the initial responders to avoid stepping in areas along the probable course taken by the perp. Simply put, walk along the walls and avoid open areas of flooring—especially non-carpeted flooring.

A series of articles will follow this post covering the most popular—yet the most effective means of recording and recovering impression evidence.

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PrinTips10-Cyanoacrylate (CA) Fuming

Cyanoacrylate or Superglue fuming is a common practice in crime labs and crime scenes.

Cyanoacrylate adhesive, better known as superglue, was first discovered by Harry Wesley Coover Jr., who was experimenting with acrylates for use in clear plastic gun-sights during World War II. He gave up because they stuck to everything they touched.

In 1951, Eastman Kodak researcher, Fred Joyner, who was working with Dr. Coover at Eastman Kodak’s laboratory in Tennessee, was testing hundreds of compounds looking for a temperature-resistant coating for jet cockpits. When Mr. Joyner spread the 910th compound on the list between two lenses on a refractometer to take a reading on the velocity of light through it, he discovered he could not separate the lenses. His initial reaction was panic at the loss of the expensive lab equipment. He ruined the machine.

In 1958, Dr. Coover saw an enormous opportunity, which led to the first incarnation of Super Glue, called Eastman 910, hit the market.

Super Glue gained fame for its incredible tenacity, but nearly 20 years passed before this product found its way into the field of forensic science. Scientists in Tokyo’s National Crime Laboratory discovered that white fingerprints kept appearing on bottles of Cyanoacrylate they kept in their lab. They subsequently discovered that white fingerprints could be developed on most non-porous surfaces, simply by exposing the invisible undeveloped latent prints to superglue fumes.

Today, cyanoacrylate fuming enjoys widespread use in the crime lab and crime scenes all over the world.

So what is going on here? Simply this: when CA fumes come into contact with moisture (about 90% of what a latent print is composed of) it polymerizes. Polymerization is a process during which relatively small molecules (monomers) combine chemically to produce a very large, chain-like molecule—known as a polymer. Many thousands of monomer units are incorporated in a single molecule of a polymer. 

In the case of latent print development, the CA fumes polymerize with the moisture of the latent print residue to form a rock-hard polymer that defies removal.

In today’s world of criminalistics, the advantages of using CA fuming are obvious: Fragile latent print ridges become virtually impervious to physical damage or destruction. Of course, the resulting prints are white but this isn’t a problem. They can be colored using regular latent print powders without fear of brushing them print away. Certain liquid dyes may be applied too, allowing for excellent photographic contrast.

Over the years, and in a sense of urgency, various methods have been employed to accelerate CA development. Merely exposing a surface to the fumes may take 8 hours or more for the results to be seen. A variety of concoctions were tried as accelerators. Treating cotton pads with sodium hydroxide was popular until the safety issues compelled many users to find other means of speeding up development.

Today, the most popular, and the safest methods used include applying heat to the CA liquid or simply squirt some CA onto a 100% untreated cotton pad. Heat is a little bit faster than the pad concept.

While CA fumes are non-toxic, they are noxious, so latent development is best performed inside an enclosure. This approach also contains the fumes in an area where they will do the most good.  Pictured below are two such developing chambers: one is portable for crime scene use, and it uses disposable plastic bags for the chamber. Heat may be applied to the glue using a small coffee warmer. The other apparatus is a glass enclosure with built in heaters.

 

 

Development is usually finished in 15 to 20 minutes in either of these approaches to development. Or if time isn’t critical, cotton pads work well with the results available in less than an hour.

Virtually any latent print powder can be used to apply a contrasting color to developed latent prints. Liquid dyes such as Ardrox, Basic Yellow or Rhodamine 6G are popular and each of these provide visible latents as well as fluorescent prints.

The advantage of using latent powders is that once the latents are photographed, they may be lifted using tapes or other special lifting devices.

Learn more about different latent processing methods by downloading the booklet: Overview of Latent Print Development Techniques. 

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PrinTips09 Adhesive-Side Latent Print Development

Developing latent prints on the adhesive side of tapes

There’s an expression among the “fit-it” community that goes like this, “If it doesn’t move and it should—use WD-40. If it moves but shouldn’t—use duct tape.” The criminal element seems to have adopted the latter advice.

Duct tape has become the bonding method of choice—investigators find it used on hostages, rape and kidnap victims and other innocent bystanders.

While many brands of duct tape feature a smooth outer surface that often harbors latent prints, the adhesive-side of this same tape may provide a bounty of latent print opportunities. Using a simple mixture of finely milled iron oxide powder and a surfactant that is brushed onto the adhesive (sticky) side of the tape, the latent print expert can quickly develop some of the most outstanding, sharp, well-defined latents he has ever seem. And no one at the moment has determined exactly what the black, soapy  goop is reacting to.

Some theorize that this developing solution is reacting to oily deposits while other experts think it may be an accumulation of dead skin cells. Regardless of why this works, the point is that it does work and latent prints from anyone who had occasion to touch the adhesive side left his/her calling card.

Here’s how to mix up and use a batch of Adhesive-Side Powder (ASP):

1. Choose the powder for best photographic contrast.

2. ASP must be premixed before use. Use a clean glass or plastic mixing bowl.

3. in a clean mixing bowl, add one teaspoon of the powder giving the best contrast against the background color of the tape. Note: Dark ASP works best on gray duct tape.

4. Add one teaspoon of eZFLO working solution to the bowl.

5. Mix the solution and the powder together using a clean brush such as the Regular Latent Print Brush (118L). Stir until the mixture has a frothy appearance.

6. Brush the mixture onto the sticky side of the tape. Allow 10 seconds for setup, and then rinse under cold, running water. Prints should be immediately visible.

Please note that ASP formulations are also available in pre-mixed solutions.

For more information on latent print development techniques and processes like ASP, download the free Overview of Latent Print Development Techniques.  http://www.sirchie.com/Assets/Manuals/pdf/LP%20Dev'mt%20Tech_TB02-102ENG-REV2E.pdf

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PrinTips 8 Small Particle Reagent (SPR)

References to Small Particle Reagent (SPR) began appearing in the literature dealing with latent print development during the late 1980s. The odd-sounding name is derived from the fact that the prime ingredient in SPR is a very finely-ground form of molybdenum disulfide. The popularity of this reagent draws from the fact that it is an ideal medium for developing latent fingerprints on wet, non-porous  surfaces. 

Molybdenum disulfide produces dark colored prints on light backgrounds. Since it was originally introduced, this process resulted in other formulations for use on dark surfaces (titanium dioxide) and a UV fluorescent formula works on virtually any background. 

Most fingerprint powders and chemical methods are ineffective on wet surfaces. SPR, on the other hand, has proven its value time and again. SPR is available commercially in a pre-mixed liquid form.  The reagent works best when sprayed on vertical surfaces, but it may also be used with tray development.

The molybdenum sulfide is mixed with a surfactant. One popular method of getting the powder into solution was the use of Kodak Photoflo®, but this product was discontinued. 

SPR seems to perform equally well on dry and wet surfaces and residue is easily washed off most surfaces. The following procedure is recommended:

SPR works well on oily windows, oxidized metals, galvanized surfaces and salt-sprayed surfaces. Use No. SPR100 Dark SPR for light-colored surfaces, SPR200 White SPR for dark-colored surfaces and SPR400UV for multicolored surfaces. Latent prints developed using this method may be lifted using standard lifting mediums once the surface has dried.

1. Select the proper reagent based upon background contrast.

2. Shake the spray bottle well to get the particles into solution. On vertical surfaces, spray above the area suspected of containing latent prints and allow it to drain down over the area.

3. For tray-development, shake the reagent well and pour into a suitable developing tray. Place the evidence in the tray. Rock the tray back and forth to permit adequate contact between the

4. Immediately after prints appear, rinse the surface with water to remove excess reagent. Do not allow the water to flow directly onto the developed prints. On vertical surfaces, apply water directly above the prints and allow it to flow across them. For tray development, remove the evidence from the developing tray and place it in a clean tray. Add running water but do not allow it to fall directly onto the developed prints

5. Photograph any developed prints as soon as possible. Be certain to include a scale. 

For more information on various latent print development methods, download the Latent Print Overview Manual.

http://www.sirchie.com/Assets/Manuals/pdf/LP%20Dev'mt%20Tech_TB02-102ENG-REV2E.pdf   

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