Fingerprint evidence not infallible

Fingerprints have been police tools for a long time, more than a century. They were considered infallible for much of that history, according to Science News.

Limitations to fingerprint analysis came to light in spectacular fashion in 2004, with the bombing of four commuter trains in Madrid. Spanish police found a blue plastic bag full of detonators and traces of explosives. Forensic experts used a standard technique to raise prints off the bag: fumigating it with vaporized superglue, which stuck to the finger marks, and staining the bag with fluorescent dye to reveal a blurry fingerprint.

Running that print against the FBI’s fingerprint database highlighted a possible match to Brandon Mayfield, an Oregon lawyer. One FBI expert, then another, then another confirmed Mayfield’s print matched the one from the bag.

Mayfield was arrested. But he hadn’t been anywhere near Madrid during the bombing. He didn’t even possess a current passport. Spanish authorities later arrested someone else, and the FBI apologized to Mayfield and let him go.

The case highlights an unfortunate “paradox” resulting from fingerprint databases, in that “the larger the databases get … the larger the probability that you find a spurious match,” says Alicia Carriquiry. She directs the Center for Statistics and Applications in Forensic Evidence, or CSAFE, at Iowa State University.

In fingerprint analyses, the question at hand is whether two prints, one from a crime scene and one from a suspect or a fingerprint database, came from the same digit (SN: 8/26/15). The problem is that prints lifted from a crime scene are often partial, distorted, overlapping or otherwise hard to make out. The expert’s challenge is to identify features called minutiae, such as the place a ridge ends or splits in two, and then decide if they correspond between two prints.

Studies since the Madrid bombing illustrate the potential for mistakes. In a 2011 report, FBI researchers tested 169 experienced print examiners on 744 fingerprint pairs, of which 520 pairs contained true matches. Eighty-five percent of the examiners missed at least one of the true matches in a subset of 100 or so pairs each examined. Examiners can also be inconsistent: In a subsequent study, the researchers brought back 72 of those examiners seven months later and gave them 25 of the same fingerprint pairs they saw before. The examiners changed their conclusions on about 10 percent of the pairings.

Forensic examiners can also be biased when they think they see a very rare feature in a fingerprint and mentally assign that feature a higher significance than others, Quigley-McBride says. No one has checked exactly how rare individual features are, but she is part of a CSAFE team quantifying these features in a database of more than 2,000 fingerprints.

Computer software can assist fingerprint experts with a “sanity check,” says forensic scientist Glenn Langenburg, owner of the consulting firm Elite Forensic Services in St. Paul, Minn. One option is a program known rather informally as Xena (yes, for the television warrior princess) developed by Langenburg’s former colleagues at the University of Lausanne in Switzerland.

Xena’s goal is to calculate a likelihood ratio, a number that compares the probability of a fingerprint looking like it does if it came from the suspect (the numerator) versus the probability of the fingerprint looking as it does if it’s from some random, unidentified individual (the denominator). The same type of statistic is used to support DNA evidence.

To compute the numerator probability, the program starts with the suspect’s pristine print and simulates various ways it might be distorted, creating 700 possible “pseudomarks.” Then Xena asks, if the suspect is the person behind the print from the crime scene, what’s the probability any of those 700 could be a good match?

To calculate the denominator probability, the program compares the crime scene print to 1 million fingerprints from random people and asks, what are the chances that this crime scene print would be a good match for any of these?

If the likelihood ratio is high, that suggests the similarities between the two prints are more likely if the suspect is indeed the source of the crime scene print than if not. If it’s low, then the statistics suggest it’s quite possible the print didn’t come from the suspect. Xena wasn’t available at the time of the Mayfield case, but when researchers ran those prints later, it returned a very low score for Mayfield, Langenburg says.

Another option, called FRStat, was developed by the U.S. Army Criminal Investigation Laboratory. It crunches the numbers a bit differently to calculate the degree of similarity between fingerprints after an expert has marked five to 15 minutiae.

While U.S. Army courts have admitted FRStat numbers, and some Swiss agencies have adopted Xena, few fingerprint examiners in the United States have taken up either. But Carriquiry thinks U.S. civilian courts will begin to use FRStat soon.

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Eyewitness identification: Minimizing the risk of error

People who witness a crime may identify the wrong person as the perpetrator for a multitude of reasons, many of which relate to basic psychology, the authors of the report write: In the room with law enforcement, a nervous witness wants to be helpful, and may strain to deliver the answer they believe the authority figure standing next to them wants to hear, reported The Appeal.

Officers want just as badly to solve the case and may unintentionally provide suggestive clues about the suspect’s identity—a phenomenon known as the “expectancy effect.” Beginning a lineup with comments like “We got the guy and just need you to pick him out,” for example, can prompt an otherwise hesitant witness to hazard a guess. 

If a witness has previously seen someone—in an earlier photo lineup, for example, or on social media—they might incorrectly believe they remember that person as the perpetrator. For this reason, the report’s authors recommend against including the same person in successive identification procedures, and urge law enforcement to discourage witnesses from doing their own amateur detective work online.

Police sketches, another staple of criminal procedurals, are another potential source of error. Research shows that people “typically process faces holistically, not feature-by-feature,” which means that a composite cobbled together from a witness’s description of individual features may end up looking nothing like the perpetrator. Yet police, with little else to go on, are likely to start looking for people who look like the composite—straying further away from the witness’s actual description, and perhaps ignoring promising leads in the process.

For the witness, the composite immediately becomes the most tangible representation of someone they may have only briefly glimpsed. During subsequent identification attempts, they may focus on a person’s resemblance to the sketch, as opposed to their recollections of the perpetrator. Because composite or sketch evidence is involved in about a quarter of DNA exonerations, the report authors recommend that law enforcement “only use them rarely and with great caution.”

Courts have long been at least somewhat aware of the shortcomings of these identification procedures. Whether police show a suspect in a photo array or alone, “it is obvious that risks of suggestion attend either form of confrontation,” Supreme Court Justice William Brennan wrote in United States v. Wade. 

And as Brennan noted in a different case, Watkins v. Sowders, it is difficult for jurors—impassive observers with no firsthand knowledge of what took place—to be skeptical of an earnest witness who saw a crime with their own eyes and swears to tell the truth in court. Quoting renowned psychology professor and memory expert Elizabeth Loftus, Justice Brennan wrote that “all the evidence points rather strikingly to the conclusion that there is almost nothing more convincing than a live human being who takes the stand, points a finger at the defendant, and says ‘That’s the one!’” 

By the time jurors file into the courtroom, though, it is far too late to warn them about all the different mistakes that can occur along the way. At that point, a suspect is an indicted defendant, and after confirming and reconfirming that the defendant is the responsible party, the witness has grown comfortable repeating this narrative to others. As a result, they may have formed a “memory” that never took place.

There are simple strategies available to law enforcement for minimizing the risks of these errors, and the report goes through them in detail: For example, whenever possible, police should conduct double-blind lineups and photo arrays, where neither the witness nor the officer administering the procedure knows who the suspect is. If double-blind procedures are impractical—for example, in smaller departments where everyone knows the suspect’s identity—officers can at least use “blinded” techniques, in which the officer cannot see which suspect or suspects the witness is viewing at any given moment. 

So-called filler lineup participants—the people asked to stand next to a suspect in a lineup—should match the elements of the witness’s description of the perpetrator, and not merely look similar to the suspect. The authors also caution against giving witnesses books of mugshots to browse, a practice that may result in witnesses over-committing to their initial identification and being less reliable during subsequent attempts. In 2001, New Jersey Attorney General John Farmer ordered law enforcement agencies to do away with “mugshot-searching” altogether and instead present witnesses with sequential, one-at-a-time lineups. The move, prompted by a U.S. Department of Justice report published two years earlier, made New Jersey the first state to embrace such a shift based on the evolving understanding of memory science. 

Using standardized instructions can reduce the likelihood of tainting the proceedings, too. The report suggests that police issue a series of caveats and reminders before each identification attempt: that the suspect “may or may not be present,” for example, and that “it is just as important to free innocent people from suspicion as it is to identify the guilty.” In 2007, lawmakers in North Carolina passed the Eyewitness Identification Reform Act in an effort to modernize identification procedures throughout the state. The act prescribes a set of initial instructions to be given to witnesses, and requires that law enforcement either conduct identifications using independent administrators who are not involved with the case, or use blinding techniques that prevent administrators from knowing whose face the witness is looking at. 

Once the witness has made an identification, the report’s authors add, police should take one final, critical step: Immediately ask witnesses for a self-assessment of their confidence, and record it without comment. Detectives should also refrain from giving any sort of suggestive feedback, even after the attempt is ostensibly “complete.” No matter what evidence later comes to light, it can be difficult to convince a witness who saw a detective pump his fist in triumph that the answer they gave was anything other than the right one.

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AG Shapiro creates statewide Conviction Integrity Unit

Pennsylvania Attorney General Josh Shapiro has announced the creation of a new, statewide office that will offer justice to people wrongfully convicted of crimes, reported the Pennsylvania Capital-Star. 

The new Conviction Integrity Unit will work with local law enforcement officials and prosecutors — especially in small counties — to reevaluate cases that ended with dubious convictions. 

Investigators will also “pursue corrections” for individuals who were wrongfully or unfairly convicted, according to the Attorney General’s website.

“We’re striving for justice, not for cases we’re dealing with today and tomorrow, but the cases we dealt with yesterday,” Shapiro said in a video announcement released Wednesday.

Shapiro has appointed Lisa Lazzari-Strasiser, the former elected district attorney of Somerset County, and a one-time public defender, to lead the new unit.

Shapiro said Lazzari-Strasiser brings “unique experience serving in a system we both agree is in need of reform.”

Conviction integrity units have proliferated in recent years amid a nationwide effort to reduce prison populations and redress past wrongs of the criminal justice system. They’re a popular tool among a crop of recently elected progressive prosecutors, who want to use their offices to reduce incarceration. 

The only other Conviction Integrity Unit in Pennsylvania, founded in 2014 in Philadelphia, has exonerated 13 defendants, according to a database maintained by the National Registry of Exonerations at the University of Michigan School of Law. 

Most conviction integrity units are located in county prosecutors offices. Only two other states — New Jersey and Michigan — run such offices at the state level, data from the registry show.

Barbara O’Brien, editor of the National Registry of Exonerations, said it’s “too early to tell” if statewide units are more effective than those run by counties. 

But she said a statewide model does provide a measure of objectivity, which can be difficult for county prosecutors to match when they’re asked to examine the work of their colleagues or predecessors. 

“You get a little removal from the people who made the original decisions,” O’Brien said. “The independence of the office is incredibly important.”

Shapiro’s new initiative will require the cooperation of Pennsylvania’s county district attorneys, who prosecute the vast majority of criminal cases in the Commonwealth.

But a spokeswoman for that group said Wednesday that they didn’t have much information about the new unit beyond what Shapiro announced publicly on Wednesday.

Lindsay Vaughn, executive director of the Pennsylvania District Attorneys Association, said Lazzari-Strasiser is scheduled to meet with members of the statewide group later this week. 

At that point, Vaughn said, “we expect to begin to hear more details and formally start the conversation on what the unit is, how it will work, what our role will be, and the complex jurisdictional issues it presents.”

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