Regardless of the potential impact “expert” testimony may provide in the courtroom, the digital expert must gain a measure of credibility for that evidence to have a degree of validity.
To gain credibility the investigator stress two vital points:
1. Cross-validation of the tools he used. Arriving at a conclusion must not be based on reliance of a single tool when investigating a cell phone. Experienced digital experts strongly recommend multiple tools for cross-validation. Cross checking the data between different tools offers a means of validation between them. Such an activity adds credibility to any evidence offered.
2. Make sure you have a solid understanding of the evidence and the methods used to collect it. Many of the investigator’s tools are quite simple to use and often require only a couple clicks to generate a detailed report. But do not become a “point and click” investigator now that the tools are so easy to use. Taking the stand without being able to speak intelligently about the methods and technology used to collect the evidence, places the investigator in the low credibility column in the minds of the jury. The more hands-on knowledge the investigator possesses relating to tool use and the information gained adds more credibility as an expert witness.
When testifying as a defense witness as an expert in federal court, the most significant change is simply that an expert witness need not disclose any prior versions of the data report or any communications had with the hiring attorney about the case and the reports generated. This eliminates a common technique of cross examination in which the expert's evolving drafts are reviewed with the idea of creating the impression on the jury that the expert was willing to change his or her opinions based on improper input from the attorney.
This is a relatively new rule in federal court, and that in many cases in state courts the older approach still prevails. Therefore, the investigator must be cognizant of the distinction between a consulting witness and a testifying witness, know your venue, determine at the outset what your role will be, and then guide yourself accordingly in terms of the information you include in your file. If you are to be a testifying witness in state court you should discuss with the attorney at the outset what his or her expectations are in terms of the type and amount of information you should maintain in your file. You may need to rely more on your memory and less on memos you created in the file.
From: New Federal Rules of Civil Procedure That Apply To Expert Witnesses by Bruce A. Olson
Apart from the expert report, probably the most important document you are likely to create as an expert witness is your Curriculum Vitae (CV) or resume. This is the first document an attorney considering hiring you will look at, and it is the first document an attorney planning to cross examine you will look at in preparation for your examination. It will invariably be included as an exhibit to your professional report. It will be attached as an exhibit to any affidavit you may submit to the court. It will undoubtedly be the first thing you are examined on at deposition or trial. Understand, therefore, that whatever you state in the CV must be the truth.
Any exaggeration or falsehood will eventually be uncovered and you will be forced to acknowledge any false statements under oath, possibly in front of a Judge and jury. Perjury charges are possible if you are not honest. The damage to your credibility by any false information in your CV, even if the expert work you've done is one hundred per cent accurate, will be incalculable.