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Hair, saliva or skin tissue at crime scenes can identify suspects or victims

But forensic evidence has faced questions over the years

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This summer marks 30 years since one of the biggest advances in criminal investigations, DNA profiling, identified a killer.

Every cell within every living creature contains DNA material. That material carries instructions that dictate everything from how tall you’ll be to what diseases you may develop, and it’s unique to you. Forensic scientists can find it in biological material left on a crime scene or body, like hair, saliva or even skin tissue.

Through DNA profiling, also known as DNA fingerprinting, scientists analyze that material and create a chart on which variations show up at different locations. These are visualized as peaks and are translated into numbers that can be matched with the DNA of other suspects or with material from missing people.

Over the years, DNA has become one of forensic science’s most powerful tools, helping to identify suspects and victims, convict the guilty and exonerate the innocent. DNA science and technology have grown so advanced that a mere touch can link someone to a crime scene.

“When I told people in 1977 in high school that I wanted to be a forensic scientist, they literally thought I was talking about voodoo and witchcraft,” said Jenifer Smith, director of the District of Columbia’s Department of Forensic Sciences and a former FBI special agent. “What DNA did in the late ‘80s and early ‘90s was sort of bring a more objective science … cool technology, molecular biology. It gave almost this credence to forensics, because now, it looks more like a science.”

Dwight E. Adams was the first FBI official to testify on DNA evidence in the United States and helped oversee the FBI’s establishment of DNA profiling rules and guidelines for labs across the country. He called DNA “the single greatest advance in forensic science.”

“The technology has improved tremendously since 1988 when it would take us 6 weeks to perform one test,” Adams wrote in an email. “Now, laboratories are performing the test in about 24 hours and able to work with samples that we could only dream about in the early days.”

Still, forensic science and DNA profiling aren’t foolproof.

Improving science

During his years in the White House, President Obama implemented several initiatives to improve forensic evidence gathering. In a 2017 Harvard Law Review article, he said they were sparked by lingering concerns from a 2009 National Academy of Sciences report, along with a rash of “high-profile exonerations of wrongfully convicted individuals that indicated that testimony exceeded the scientific capabilities of the technique.”

“Contrary to the perception of TV dramas, forensic science disciplines are subject to varying degrees of uncertainty and misinterpretation,” Obama wrote.

Forensic evidence pinning a suspect to the scene of a crime can be powerful in the courtroom. But scientists agree that when investigators testify about that evidence, they haven’t always emphasized to the jury that science can make mistakes, such as DNA contamination in labs or DNA transferred from one crime scene to another.

One of Obama’s initiatives launched a review of FBI testimony in cases. Another brought together scientists, law enforcement officials, judges and lawyers to create the National Commission on Forensic Science. Both of these initiatives were ended in April by Attorney General Jeff Sessions, who said the Trump administration would seek its own path toward improving criminal investigations under a new task force.

Some investigators said that over the years, funding has not kept up with the demand for evidence analysis, and labs are overwhelmed.

“Forensic science has been dealing with a resource problem,” said former investigator John M. Collins Jr., whose Forensic Foundations Group works to educate lab technicians.

Indeed, crime labs around the country now process over 3 million requests per year, one-quarter of which is DNA profiling, according to the Bureau of Justice Statistics.

Here are a few notable cases in which DNA evidence made a mark.

30 years since an early test

In 1986, authorities in Leicester, England, were investigating the rapes and murders of two young women. A suspect confessed to the crime involving one woman but not the other. Convinced the two crimes were linked, investigators sought the help of Dr. Alec Jeffreys, a geneticist who developed techniques to visualize bands of DNA in his lab.

With Jeffreys’ help, authorities analyzed the DNA of hundreds of men living near the crime but found no match. But the analysis also cleared the man who had confessed. In 1987, authorities found that local baker Colin Pitchfork had avoided taking the test. His sample was a match for both killings, and under pressure from DNA evidence, he confessed to the crimes.

Exonerated by DNA

In 1989, Gary Dotson became the first person exonerated because of DNA testing. He’d been behind bars for over a decade after a woman accused him of rape in 1977.

Investigators used blood-type and hair analysis to convict him, but he appealed for years, until DNA testing could be applied to material still held from the case. DNA cleared him, and he won his release. Testing linked the evidence to the accuser’s then-boyfriend, and the woman admitted she’d made up the rape.