For example, the victim may know the suspect had stubble on his face because she felt it but never actually saw it, which is a tactile memory. Or she may have smelled alcohol or cigarettes (olfactory memory) or heard the muffler of a car (auditory memory).
“Having the victim recount all of these memories greatly increases the thoroughness of the description of the entire event, resulting in a more accurate likeness of the suspect’s face,” adds Birdwell.
The interview process is best conducted in a private setting where the forensic artist can be alone with the victim and take as much time as necessary to complete and obtain the drawing.
When some police agencies don’t have access to or can’t afford a forensic artist, they sometimes opt for a commercial computerized sketching system. These work up to a point, but some programs only hold a limited number of facial features from which the witness must choose when constructing the suspect’s face.
“By contrast, a freehand forensic composite artist can literally add anything to the image, and can also make even the smallest of changes the witness may like to include,” Birdwell says. “A competent forensic artist never wants to limit her witness’ statements by not being able to fully develop the image the witness holds in her mind.”
Another downside to some commercial systems, she continues, is that many of the features used in these systems are photo-realistic. A composite drawing of a person-of-interest is best if it still retains some sketch-like qualities, because that broadens the interpretation of that face by the viewer.
The more “photographic” the image looks, the more the public views it to be ‘real’. The problem with images being too realistic is that viewers may eliminate possible persons in their minds as being a match to the drawing because every detail they hold in memory may not be exactly like the too-real image.
On the other hand, if the composite drawing is viewed as a sketch, the public understands it is merely a suggestion of the suspect’s appearance. “Humans recognize faces holistically,” Birdwell says. Which is to say humans take in the image as a whole, without measuring small distances between features.
Sometimes police agencies that purchase a software sketching package may not have a person who has been trained on both the drawing process or cognitive interviewing because the agency seldom needs composite drawings. Instead, the agency calls someone to run the software when they need a drawing.
One problem with this approach, according to Birdwell, is that the victim may not get the benefit of the detailed interview necessary to probe all areas of memory, including tactile, auditory, and olfactory, which may result in a less detailed rendering of the face.
The solution of course would be to open up more full-time forensic art positions—an unlikely prospect in an era of diminishing budgets, no matter how valuable the services might be.
“These services need not be limited to composite drawings of persons-of-interest, but should also include other genres of forensic art, such as age-progressed and age-regressed facial images, courtroom exhibits, image clarifications from video, and postmortem artwork that reconstructs facial features from skeletal remains to help identify unknown decedents,” says Birdwell.
A new wrinkle
One new wrinkle has been added to the forensic art process that promises to give composite drawings even more forensic utility.
A team of researchers at Michigan State University has developed software that takes facial composites drawn by forensic artists, and then automatically searches photographic mug shots stored in law enforcement databases for matches, significantly accelerating the suspect identification process.
“The forensic composite procedure used [publishing a sketch and waiting for volunteers to come forward] to identify a suspect is slow and tedious, and there is no guarantee of identifying the suspect,” says Anil Jain, a Michigan State professor of Computer Science and Engineering.
He says it would be desirable if police could automatically compare the suspect’s composite facial sketch drawn by the forensic artist to the millions of mug shots in state and federal law enforcement databases. The problem is current facial recognition software systems do not perform well in matching a sketch to a photo.