Tag Archives: forensic

Bacterial DNA Profiling

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 Finding DNA

Earlier this month, researchers at Washington University School of Medicine (St. Louis) and at the European Molecular Biology Laboratory (Heidelberg, Germany) reported a new type of DNA profile: DNA profiles from human gut bacteria. The researchers analyzed microbial DNA in 252 stool samples from 207 individuals, focusing on 101 species of microbes commonly found in the intestine. They found many types of DNA differences, the sort of differences that generate unique DNA profiles. For 43 subjects, the researchers collected two stool samples one month to six months apart. The scientists found little variability in the microbial DNA. In short, they discovered variability in DNA profiles between subjects and consistency in DNA profiles in subjects over time.

“The microbial DNA in the intestine is remarkably stable, like a fingerprint,” said George Weinstock, associate director of The Genome Institute at Washington University. “Even after a year, we could still distinguish individuals by the genetic signature of their microbial DNA.”

It’s not immediately obvious how this discovery could be incorporated into a crime story. But, if you can do it, then consider yourself on the cutting edge.

A more apparent application of bacterial DNA profiling to mystery stories is found in the discoveries of Noah Fierer and his colleagues at the University of Colorado in Boulder. They found that a typical human hand shelters about 150 species of bacteria. The types of bacteria living on skin vary greatly. In a 2008 study, they identified more than 4,700 different bacteria species living on the hands of 51 people. Yet only five species lived on the skin of every participant of the study.

In 2010, the researchers reported that computer users leave DNA traces of bacteria on computer mice and keyboards. These DNA traces more closely match the DNA of bacterial colonies that inhabit the hands of the individual who used the computer, compared with bacterial DNA traces of randomly selected people. The researchers obtained useful samples of bacterial DNA two weeks after a person touched computer equipment.

Digging Mona Lisa

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Who posed for Leonardo da Vinci’s “Mona Lisa”? CNN’s Ben Wedeman reported that scientists may soon find the answer to this age-old question.

In Florence, Italy, old records indicate the burial site for Lisa Gherardini, the second wife of Florentine silk merchant Francesco del Giocondo. That’s Lisa as in Mona Lisa. The records led to a derelict building standing on the remains of a Franciscan convent.

Silvano Vinceti and his team exhumed and identified Lisa Gherardini’s remains. Bone fragments will be sent to universities, where researchers will analyze DNA and compare the DNA profile with DNA profiles of two confirmed relatives of Gherardini.

“Once we identify the remains,” Vinceti told CNN, “we can reconstruct the face, with a margin of error of 2 to 8 percent. By doing this, we will finally be able to answer the question the art historians can’t: Who was the model for Leonardo?”

While these efforts may reveal the true face of the Mona Lisa model, the mysterious smile is another matter. The smile did not belong to Gherardini, Vinceti claims. Rather, da Vinci lifted the smile from his longtime assistant, Gian Giacomo Caprotti.

DC’s New Crime Lab

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Firearms analysis

Firearms analysts keep a reference library of bullets to match bullets recovered from crime scenes. Source: Katye Martens/Stateline. (Stateline is a nonpartisan, nonprofit news service of the Pew Center on the States that provides daily reporting and analysis on trends in state policy.)

On November 27, the Pew Center on the States website posted Maggie Clark’s article, “D.C. Crime Lab: An Experiment in Forensic Science.” The new crime lab reflects many of the recommendations from the National Academy of Sciences’ 2009 report on the state of forensic science. For example, the lab is staffed only with civilian scientists.

Many jurisdictions have crime labs tied to the local prosecutor’s office or police department. D.C. Council member Phil Mendelson told Clark that close connections between crime labs and police can expose labs to harsh criticism. “If the crime lab is within the police department,” Mendelson said, “defense attorneys could say to an analyst, ‘well, you work for law enforcement, you’re just proving the police officer’s case.’ It’s better for the justice system when forensic analysis is done by a separate agency.” The D.C. lab is an independent lab; its director answers to the Deputy Mayor for Public Safety.

Dr. Max Houck, director of the D.C. Department of Forensic Science, said that D.C.’s civilian-led crime lab can lead the way to similar changes in other U.S. crime labs.

“We need a national strategy on forensic science,” Houck said. “Here, we are running the agency as a science-based organization and as a peer with other agencies like the medical examiner or law enforcement with the focus really being on the science.”

A science-based crime lab operating independently of a police department is not a new idea. In 1914, Sir Lomer Gouin, premier of Quebec, announced the establishment of the Laboratoire de Recherches Medico-Legales. It was the first forensic lab in North America.

ME Time

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Morgue

Have you noticed how detectives can call their favorite medical examiner minutes after they left a crime scene for a report? Does this timeframe seem too brief for your own story? In real life, detectives can wait a considerable time before they see anything from a medical examiner.

On September 21, 2012, The New York World posted an article about these delays in New York: “More Work, Fewer Staff Add Up to Longer Waits for Medical Examiner Reports.” For example, the Medical Examiner office needed about 46 days to provide DNA test results in sexual assault cases. Toxicology reports required about 60 days. Can’t detectives grab a bite after visiting a crime scene and then call the ME for autopsy results? Sure, but they shouldn’t expect an answer. An autopsy takes about 70 days to complete.

So, if you want to delay the appearance of test results in your story, then don’t worry about it. Any delays will just make the story more realistic.