How Police Sketches Work

Before forensic artists can begin composing police sketches, they obviously need an idea of what their subjects look like. For that reason, the eyewitness interview is the most important step in the police sketch process [source: Taister]. Officers or artists doing the questioning need to understand what to ask and how to approach interviewees to cull the most accurate information, since the human memory for faces can be easily fooled. Often, people have a difficult time recalling specific facial features, and the more time that lapses between a crime and the police sketch interview, the fuzzier those memories become [source: Raeburn].

Depending on the crime and the person being interviewed, police sketch sit-downs can last hours. To get an idea of how these question-and-answer sessions are conducted, consider a 2007 study examining people's ability to describe faces for creating forensics facial composites. It broke down the cognitive interview into three phases: rapport building, free recall and cued recall [source: Frowd et al.].

Rapport building simply involves casual conversation -- "Hi, how are you?" -- in an effort to relax the interviewee. Next, the interviewee is asked to recall as many specific details about the criminal as possible. Often, participants begin by discussing hair and general face shape [source: Frowd et al.]. During the last step, cued recall, the forensic artist will ask the interviewee about any defining features they don't immediately remember. At that point, it might be helpful to jog the interviewee's memory with mug shots of previously incarcerated criminals. That way, seeing a similar nose or eyes or jaw line might spark a flashback. Forensic artists may also keep a catalog of celebrity portraits around since the famous faces can spark visual cues as well [source: Raeburn].

While forensic artists keenly focus on minute facial features, former New York Police Department artist Stephen Manusci notes that victims are more apt to provide broader descriptions, such as a "horse face" or "bug eyes" [source: Lichtman]. The role of an adept artist is to break down, or "decode," those vague generalizations into a collection of discrete facial characteristics. That doesn't mean the forensic artist should ever drill someone for more characteristics; pressuring the interviewee might stifle, rather than stimulate his memory [source: Muench]. As the sketch takes shape, interviewees will also begin to either show recognition or point out discrepancies.

Drawing a police sketch by hand clearly requires a degree of artist talent, but it doesn't necessarily demand a degree from art school. Depending on the size of the police department, forensic artists may or may not be full-time employees. In small-town departments, a patrol officer with a knack for drawing may actually volunteer for the role, while larger, better-funded agencies may employ civilians formally trained at the FBI's forensic facial imaging laboratory or other forensic art training programs [source: Echaore-McDavid and McDavid].

The police sketching process also varies by forensic artist. For instance, former NYPD forensic artist Stephen Manusci takes the old school pencil and paper route, refining the face as needed with input from victims or eyewitnesses [source: Lichtman]. Roderick Scratchard, forensic artist with the Philadelphia Police Department, takes the opposite route. First, he creates a computer-generated composite based on photos of faces and features that interviewees have selected. Then, he draws the final police sketch by hand based on that computer composite, tweaking the appearance as requested [source: Avril].

Computers have played a role in police sketches since the 1960s, with the arrival of the identi-Kit composite software. Police departments without the resources to retain a bona fide forensic artist could instead purchase identi-Kit -- and now a host of other programs -- to automatically generate facial composites by selecting from a gallery of profiles and traits. Reliance on computers has proven controversial, however, as studies have shown that hand-drawn police sketches often turn out more accurately than computer-only composites [source: Avril]. Newer programs do a better job at producing more nuanced mug shots. Hearkening back to Bertillon's cross-indexing to pinpoint repeat offenders, a computer program developed at Michigan State University in 2011 digitally analyzes hand-drawn composites and compares them to photographed mug shots stored in law enforcement databases. Due to high recidivism rates, the highly publicized technology could help officers identify suspects more quickly. Nevertheless, the FBI isn't impressed by any technological advances. Due to the anecdotal accuracy, when it comes to the paper versus computer quandary, hand drawn composites are a must-have in the agency's book [source: FBI].

But whether a facial composite is drawn by a person or a computer, the question of whether it looks anything like the person who committed the crime remains sketchy.

Forensic artists who have drawn their fair share of facial composites will probably confess an awkward truth about police sketches: They aren't very accurate. By one estimate, hand-drawn composites by trained artists are roughly 9 percent accurate in terms of producing a recognizable likeness to a suspect [source: Avril]. And as we mentioned previously, computer-generated composites statistically tend to be of even poorer quality than hand-drawn sketches, with around 5 percent accuracy [source: Avril].

And it's not necessarily a question of the forensic artists' skill. Even if Leonardo da Vinci were creating police sketches, accuracy issues would still crop up. The major roadblock to creating spitting images of suspects rests not in the forensic artist's hand, but the victim's or witness' memory retrieval processes. If you think about a human face as a chess set, our brains don't capture that image as a collection of knights, pawns and other discrete pieces, which would rely on our recall memory -- memory that requires no priming, such as being shown a picture of someone and asked to identify it. Instead, our brains summon our recognition memory, which relies on cues, such as spotting someone on the street, in order to form the associations that allow us to put, for instance, names with faces. For that reason, we might all know what Brad Pitt looks like and easily identify him strolling down the street, but we'd have a much harder time describing his appearance from scratch.

The violence, stress and trauma of being victim to a crime, as well as the time lapse between the crime and the police sketch interview only muddies recollections [source: Raeburn]. Depending on the circumstances, a criminal's face may never make it through the brain's memory-making process. To store a memory lock-tight, the brain must encode a face, consolidate all of the information about that face (eyes, nose, facial hair, etc.) and catalog it alongside similar-looking faces already stored away upstairs. Cementing that memory for later retrieval during an interview further entails retracing neural pathways by thinking about that face, which might be the last thing a frightened victim wants to do. How easy is it to complete that mental workout in the time it takes to get mugged at gunpoint? Not very.

So why spend time and resources on police sketches if they're neurologically doomed for inaccuracy? Forensic artists argue that the role of police sketches isn't to construct a perfect portrait of the perpetrator. The point of police sketches is to publicize crimes, attract leading clues and get the public looking out for suspicious persons [source: Lichtman]. That's why the artists will highlight standout features -- a tattoo, scar, facial hair -- that might jump out at passersby. After all, happenstance led an Oklahoma State Trooper to pull over Timothy McVeigh less than two hours after the Oklahoma City bombing. But it was that composite sketch distributed by the FBI that eventually tipped off the law enforcement officers that they had a most-wanted criminal on their hands.

Though they're quite common, police sketches are one of the most controversial criminology techniques, since they rarely result in a spitting-image representation of a criminal suspect. For that reason, I wanted to get to the bottom of whether police sketches serve any useful law enforcement purpose and whether advanced technology holds any promise for fine-tuning the portraiture process. The U.S. Department of Justice is funding preliminary research into DNA phenotyping, which could potentially offer clues to criminals' appearances based on DNA samples of hair or blood collected from crime scenes. But in the meantime, forensic artists must rely on a combination of strategic interview tactics and portraiture skills to cobble together suspects' physical features. For all of the high-tech forensics techniques showcased today in crime dramas on TV, tracking down a criminal's face remains a surprisingly primitive practice at most law enforcement outposts.

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