Testimony as Teaching: Visual Aids
Written by Hillary Moses Daluz   


An excerpt from:
Courtroom Testimony for Fingerprint Examiners

This article appears in the September-October 2021 issue of Evidence Technology Magazine.
You can view that full issue here.

HUMANS ARE INHERENTLY VISUAL. The adage states, “a picture is worth a thousand words.” This maxim holds true for the successful teacher as well as the successful expert witness. Visual aids such as charts, photographs, diagrams, and slide presentations are effective teaching tools. Consider this fictitious expert testimony from a crime scene investigator describing where two victims and one item of evidence were located at a crime scene:

The knife, item #1, was found in the street on 14th Street near the curb, approximately 5.18 meters west of the northwest corner of Alexander Way and 14th Street. It was located approximately 0.24 meters south of the curb and approximately 5.8 meters east of victim number two’s vehicle. Victim number two was found lying prone in the middle of 14th street approximately 4.7 meters south of the vehicle. Victim number one was found lying supine in the west driveway of the parking lot for Frankie’s Fish ‘n Chips and the Corner Store, perpendicular to the sidewalk along 14th Street, approximately 12 meters east of the northeast corner of University Avenue and 14th Street…

Imagine hearing this description in the role of a juror. Would this description of the locations of victims and the item of evidence be clear? Now consider the use of a visual aid. In this case, the visual aid is the crime scene diagram, Figure 1. Which is a more effective presentation of the data: the verbal description or the diagram? The diagram is more effective as it allows the jurors to see the special relationships visually rather than attempting to keep track of the verbal description while forming a mental picture of the scene. Another visual aid that would be useful in the example above would a photograph, or multiple photographs, of the scene.

Figure 1. A crime scene diagram is an example of a visual aid that may be a more effective representation of the scene than a verbal description.

A visual aid is not a replacement for testimony but instead is used as a teaching tool to enhance the expert witness’s explanations and descriptions. The visual aid utilized must be applicable to the data it represents. Graphs, for example, can be formulated in different ways. Bar graphs indicate differing quantities, whereas pie charts indicate proportions. Line graphs demonstrate trends over time. Once the appropriate chart is selected, the data must be simplified so that it does not confuse or overwhelm the jurors. All unnecessary information should thus be omitted. While data charts and graphs are not often applicable to a fingerprint examination, there are certain visual aids that should be considered. The most common visual aid for the fingerprint examiner is the fingerprint comparison chart. This chart is critical for scientific transparency. The modern forensic scientist must document each step in the analysis and be able to demonstrate how a conclusion was reached (Figure 2).

Figure 2. A fingerprint comparison chart is an effective and transparent method for explaining the fingerprint examiner's source identification conclusion to a jury.

Some forensic scientists have expressed concern about giving jurors too much information. What if a juror sees minutiae that were not marked in the chart? What if there is distortion in the latent print which makes it appear different from the exemplar? This is easily remedied, as it is the duty of the fingerprint examiner, as an expert witness, to explain discrepancies jurors may notice. In fact, some fingerprint examiners purposefully mark a select number of minutiae and indicate that not all minutiae have been marked in the chart. The jurors will then find it an interesting challenge to attempt to locate more minutiae. This is an effective way to capture and maintain the jurors’ interest.

Fingerprint charts are prepared in a variety of formats. The preferred format is digital. Many automated biometric identification systems (ABIS) include charting software. If charting software is not available, commercial photo editing software such as Adobe Photoshop is an excellent resource for creating fingerprint comparison charts. Fingerprints can be charted in two separate windows and then be saved as a digital file with screen capture software. If this method is utilized, ensure that the original image is saved in a secure location in a lossless format and that a working copy of the original image is manipulated. The enhanced image should be saved in a way that makes it clear the image is a copy of the original, not the original image.

Non-digital options for fingerprint comparison chart presentations include paper handouts or poster boards. Handouts can also be utilized for jury education. They can be duplicated and distributed to jurors, though many jurisdictions have guidelines about how this is accomplished. Some jurisdictions may not allow handouts to be distributed to jurors. It is important to consult your supervisor and the attorney for the case prior to utilizing this method. Figure 3 demonstrates a one-page handout that can be used to educate jurors about fingerprint examination. Another non-digital option is to utilize a poster board, either traditional or bi-fold style. The questioned print and exemplar print are charted on each side of the fold and demonstrated to the jury. Regardless of the presentation method, the fingerprint examiner should be prepared to testify to anything visible in the image such as distortion; the varied appearance of certain minutiae (a point that appears as a bifurcation in one print and an ending ridge in the other due to deposition pressure, for example); the location and directionality of the print as it was found and the minutiae plotted.

Figure 3. A one-page handout with images demonstrating the foundations of fingerprint examination.

Digital fingerprint charts are often displayed in the courtroom using presentation software. While its prevalence makes it familiar and straight-forward for most professionals to use, it is also frequently misused or overutilized. Entire books have been written about creating successful digital slide presentations. Digital presentations often focus on the style over the content, “replacing clear thought with unnecessary animations, serious ideas with ten-word bullet points, substance with tacky, confusing style” (Mauriello, 2020). In a comprehensive review of the available literature, Craig and Amernic (2006) found that while students prefer to be taught via Microsoft PowerPoint, this preference does not correlate with an increase in academic performance.

While digital presentation software is ubiquitous and useful in many professional and academic situations, it also suffers from several potential formatting and content pitfalls, inspiring the phrase, “death by PowerPoint” (Phillips 2014). A general guideline is to keep digital slide presentation formatting as simple as possible. Background patterns, unnecessary animations (such as characters or slide transitions), florid fonts, and clip art are not recommended. The most successful digital presentations have a dark background, preferably solid black, with light-colored font in white or gold. While paper documents are white with black writing, digital slides are large-format and brightly lit, and thus should be color-reversed to avoid eye strain. A white slide background with black font is too bright on an oversized screen.

The selected font should be simple and easy to read, such as Helvetica. It should be large enough for jurors to read clearly with a font size no smaller than 24 point. Contrary to common practice, the font size of the content should be larger than the font size of the title at the top of the slide (Phillips 2014). The human eye is drawn to the larger, brighter object on the screen. As the content is more important than the title, it makes sense to use a smaller font for the title of the slide and a larger font for the content (Figure 4).


Figure 4. The slide above demonstrates how the eye is drawn to the larger font size of the slide's title rather than the content. In the slide below, the content is displayed with a larger font size than the title, highlighting the contents for the audience.

The content of a digital slide presentation is just as important as the formatting. Each slide should be concise with few words capturing one core idea rather than full sentences the jurors will have to read. If a juror is reading a slide, he cannot simultaneously listen to the expert witness testimony. A good rule of thumb is to include no more than six items per slide and to only include information that augments the testimony (Mauriello 2020) (Phillips 2014). The explanations and any elaboration regarding the content should be left to the presenter. Images are more impactful than words on a slide presentation. For example, a fingerprint examiner may choose to present a slide with an enlarged image of a bifurcation and an ending ridge in order to teach jurors about minutiae. Another slide might include an image of each major pattern type: arch, loop, and whorl.

People generally cannot multitask, despite assertions to the contrary on resumes and at job interviews. Jurors can therefore focus on only one thing at a time: either a visual aid or the expert witness. If a digital presentation is utilized, the jurors’ attentions will be split between the words or images on the screen and the expert witness’s testimony. For those with anxiety triggered by public speaking, the use of a visual aids takes some of the focus off the speaker, easing that apprehension. The expert witness should never be over-reliant on technology, as there is always the possibility of experiencing technological difficulties. Technology should complement courtroom testimony, not dominate it.

Some forensic experts utilize dry-erase boards or oversized notepads on easels in order to draw as they testify. For example, the fingerprint examiner may draw an ending ridge and bifurcation while describing how fingerprint comparisons are done. The benefits of this method are that it is an interactive, captivating style of presentation. It also allows the expert witness to come out from behind the witness stand and connect more effectively with the jurors. The drawbacks are that it is easy to make a mistake and have to start a drawing from scratch. If this method of presentation is employed, it must be practiced ahead of time. It is also not allowed or preferred in certain jurisdictions. If it is allowed, the expert must ask permission to stand up and move from the witness area to the demonstration area. If the forensic expert chooses this method of presentation, they should take care not to turn their back to the jury.

If none of the visual aids detailed above are permitted in your jurisdiction, recall that body language is a key aspect of a confident, engaging demeanor. The fingerprint examiner can use hands as visual aids for a multitude of topics. The hands can be used to indicate size, such as the approximate length of an item processed for fingerprints. They can be used to indicate the location and directionality of prints, such as to demonstrate how palm prints may be deposited on a windowsill that has been determined to be the point of entry for a burglary. Hand gestures can indicate the shape of ridge flow (arch, loop, and whorl) or point out the various areas of the palm (hypothenar, thenar, and interdigital area). Fingerprint experts can also encourage jurors to observe the friction ridges on their own hands. Not only does this build rapport with jurors but it also captures the jurors’ attention and encourages interactive participation in the testimony.

Regardless of the presentation media used (apart from using one’s hands), visual aids are discoverable. Both the prosecution and the defense in an adversarial system have the right to review and critically analyze any work product produced by the fingerprint examiner. This also includes any visual aids prepared for court. If you plan on using any visual aids, they must be prepared far enough ahead of time to be approved by both your supervisor and the prosecuting attorney, as well as provided to the defense for review.

About the Author

Hillary Moses Daluz is a latent print examiner with extensive and diverse experience within the forensic science community. She is the author of Fundamentals of Fingerprint Analysis, Second Edition (CRC Press, 2018) and the Fingerprint Analysis Laboratory Workbook, Second Edition (CRC Press, 2018). She began her career as a police identification specialist with the City of Hayward Police department in Hayward, California. After earning a Master of Science degree in Forensic Science from the University of California, Davis, she deployed to the Joint Expeditionary Forensic Facility at Camp Victory in Baghdad, Iraq as a latent print examiner. After returning stateside, she became a member of the faculty in the Forensic Sciences program at Chaminade University of Honolulu, teaching at the undergraduate and graduate level. She has worked in a variety of forensics positions including as an instructor for Tri-Tech Forensics, Senior Latent Print Technician with American Systems, and Forensic Specialist with Forensic Identification Services. She is a member of the Board of Directors for the International Association for Identification (IAI), an affiliate member of the OSAC Friction Ridge Subcommittee, a member of the Florida Division of the IAI and a member of the Chesapeake Bay Division of the IAI.


Coursey, D. 2003. What’s Wrong with PowerPoint—And How to Fix It? AnchorDesk. http://www.zdnet.com/anchordesk/stories/story/o,10738,2914637,00.hml (accessed 30 Jan 2020).

Craig, R., and J. Amernic. 2006. PowerPoint presentation technology and the dynamics of teaching. Innovative Higher Education. 31(3):147–160.

Mauriello, T. 2020. Public Speaking for Criminal Justice Professionals: A Manner of Speaking. CRC Press: Boca Raton, FL.

Phillips, D. 2014. How to Avoid Death by PowerPoint. TEDx Stockholm Salon. https://www.youtube.com/watch?v=Iwpi1Lm6dFo (accessed 10 June 2020).

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