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Correcting Injustices with DNA

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DNA can be key to exoneration

 

The Innocence Project at Yeshiva University and other programs use DNA evidence to exonerate people wrongfully convicted of crimes. According to the Innocence Project website, the common causes of wrongful convictions include eyewitness misidentification, improper forensic science, false confessions, government misconduct, unreliable informants or snitches, and bad lawyering. Details about these causes and a geographic distribution for each cause within the United States can also be found on the website.

If DNA exoneration is a key point in your plot, you may want to peruse the U.S. Department of Justice’s report, “Post-Conviction DNA Testing and Wrongful Conviction.” It was published in June 2012, and it’s available from the National Institute of Justice website.

Errors in the Digital Age

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Fingerprint

 

In the digital age, fingerprints are recorded using scanners, rather than ink pads and paper. As with any new technology, the question of quality control arises. Variables ranging from a subject’s dry skin to a dirty sensor plate can produce an image that could yield an incorrect match with a fingerprint on file. The U.S. National Institute of Standards and Technology (NIST) developed a program that judges the quality of a scanned fingerprint, and indicates if a fingertip should be rescanned. NIST released the software to U.S. law enforcement agencies and biometrics researchers.

Often, films and TV shows depict a technician who declares a fingerprint match based on computer analysis. In reality, an expert makes the final decision about a match by comparing fingerprints. This eliminates computer error, but introduces human error.

The National Institute of Justice and NIST assessed the effects of human factors on forensic latent print analysis and drafted recommendations to reduce the risk of error. A copy of the 2012 report, “Latent Print Examination and Human Factors: Improving the Practice through a Systems Approach,” is available from the National Institute of Justice website. The NIJ also offers a flow chart that shows the Analysis, Comparison, Evaluation, and Verification (ACE-V) process for latent print examination used in national forensic crime labs.

Kasey Wertheim and Melissa Taylor’s article, “Human Factors in Latent-print Examination,” is another good source for information on causes for fingerprint analysis errors. The article was published in the January-February 2012 edition of Evidence Technology Magazine.

A Pioneer of Fingerprint ID

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Fingerprint card of Francesca Rojas.

Fingerprint card of Francesca Rojas, 1892. Source: National Library of Medicine.

On the evening of June 19, 1892, Francesca Rojas burst into a neighbor’s shack on the outskirts of Necochea, a small coastal village in the province of Buenos Aires. She cried that Velasquez, a laborer at a nearby ranch, had murdered her children. Velasquez had wanted to marry Rojas, but earlier in the day, she told him that she planned to marry a younger man. According to Rojas, Velasquez became furious and swore revenge.

A search of Rojas’ hut revealed the bodies of a young boy and girl with fatal head wounds. The police arrested Velasquez and questioned him. The farm hand refused to confess, even under torture. Meanwhile, rumors about Rojas began to surface. Gossipers said that a young man had told Rojas that he would marry her if she did not have the two children. Wondering if Rojas might be the murderer, the police sought help from La Plata regional headquarters.

La Plata Police Inspector Eduardo Alvarez reexamined the Rojas hut. He noticed a dark, brownish mark on the door of the children’s bedroom: the imprint of a bloodstained human thumb. Alvarez knew about the value of fingerprints. He borrowed a saw and cut a piece of the door that contained the finger mark. Alvarez returned to La Plata with the evidence and with Rojas in custody.

At the police station, he rolled Rojas’ right thumb on an ink pad, and then pressed it on a sheet of paper. Then, he called in Juan Vucetich, head of the La Plata Bureau of Identification and Statistics. Vucetich had become interested in fingerprints after reading Francis Galton’s book. He performed his own fingerprinting studies and devised a classification scheme. After Vucetich matched Rojas’ inked print with the bloody thumbprint on the door, Rojas admitted to killing her children. The case has been hailed as the earliest murder investigation solved with fingerprints.

With further research, Vucetich perfected his fingerprint identification system and published the details in his book, Dactiloscopía Comparada (1904). The Vucetich system is still used in most Spanish-speaking countries.

GSR Speaks Again

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Traditionally, gunshot residue contained gunpowder residues (such as partially-burned or unburned gunpowder) and lead residues. However, an increasing number of ammunition manufacturers produce ammunition that contains little or no lead. This change is good for the environment, but creates a challenge for criminal investigators, because crime labs test for gunshot residue by detecting the presence of lead, barium, and antimony.

During June 2012, forensic researchers at Florida International University announced a new technique that can potentially link a suspect to fired ammunition by identifying the chemical signature of the powder inside a bullet. In this approach, a chemist analyzes the chemical composition of a bullet’s smokeless powder. The method reveals the particular formula of the smokeless powder, which further identifies the manufacturer of the powder.

“Crime labs all over the country are faced with the reality that their only way to analyze whether a gun was fired by a suspect may become obsolete,” said chemistry Professor Bruce McCord in a press release. “Our discovery is not only more accurate, but it can determine the type of gunpowder used in a crime even if the gun is never recovered.”