How reliable is DNA in identifying suspects?

[flashl]

State crime lab analyst Kathryn Troyer was running tests on Arizona's DNA database when she stumbled across two felons with remarkably similar genetic profiles.

The men matched at nine of the 13 locations on chromosomes, or loci, commonly used to distinguish people.

The FBI estimated the odds of unrelated people sharing those genetic markers to be as remote as 1 in 113 billion. But the mug shots of the two felons suggested that they were not related: One was black, the other white.

In the years after her 2001 discovery, Troyer found dozens of similar matches -- each seeming to defy impossible odds.

As word spread, these findings by a little-known lab worker raised questions about the accuracy of the FBI's DNA statistics and ignited a legal fight over whether the nation's genetic databases ought to be opened to wider scrutiny.

...

At stake is the credibility of the compelling odds often cited in DNA cases, which can suggest an all but certain link between a suspect and a crime scene.

LA Times

[TechBear_Seattle]

1. K & R n/t

[theoldman]

2. Their DNA was similar but not a match.

Unless you understand DNA you will think that the wrong person can be convicted. Even identical twin's DNA is not a perfect match.

[stray cat]

3. Isn't 12/12 considered a match? or is the required match that much below that.

The segment on 60 minutes was more a case if the DNA is extremely similar can you use that information as a basis to test a family member who might be responsible for the crime.

[midnight]

4. DNA sequencing, are as prone to laboratory errors

One fact that remains, however, is that molecular tests, including highly standardized methods such as DNA sequencing, are as prone to laboratory errors (technical or human) and/or interpretation errors as any other laboratory test. In this issue of Clinical Chemistry, the authors of two Europe-wide studies on external quality assessment (EQA) for DNA sequencing report their findings (4)(5), and both show considerable variations in expected outcomes and some wrong genotyping results (diagnostic errors). http://www.clinchem.org/cgi/content/full/52/4/557

[theoldman]

5. You are correct.

The DNA does not lie. It's the lab technicians that can screw up especially if the results are close. Fortunately most of the time it is not close.

[TZ]

9. Yep.

This is why duplicate testing should always be done. I am familiar with the technology used in DNA testing..Its pretty reliable for the most part..but like most bioassays it is quite prone to in lab errors.
I'm not positive but I think there are different tests that can be done for different loci...Which is probably a better way to solidly identify suspects..Multiple assays...
Overall the technology is very good..human error is the problem here.

[flashl]

6. Is this a challenge to practices like the one below?

From DNA of Family, A Tool to Make Arrests

He was a church-going father of two, and for more than 30 years Dennis Rader eluded police in the Wichita area, killing 10 people and signing taunting letters with a self-styled monogram: BTK, for Bind Torture Kill. In the end, it was a DNA sample that tied BTK to his crimes. Not his own DNA. But his daughter's.

Investigators obtained a court order without the daughter's knowledge for a Pap smear specimen she had given five years earlier at a university medical clinic in Kansas. A DNA profile of the specimen almost perfectly matched the DNA evidence taken from several BTK crime scenes, leading detectives to conclude she was the child of the killer. That allowed police to secure an arrest warrant in February 2005 and end BTK's murderous career.

The BTK case was an early use of an emerging tool in law enforcement: analyzing the DNA of a suspect's relatives. In the BTK example, police had a suspect and were looking to tie him to the crime. But now, states are moving to conduct familial searches of criminal databases, looking for close-to-perfect matches with DNA from crime scenes. A partial match with a convicted criminal could implicate a brother or daughter or father of the convict. Such searches, advocates say, constitute a powerful law enforcement tool that, experts say, could increase by 40 percent the number of suspects identified through DNA.


Washington Post

[flashl]

7. Related article ...

DNA matches aren't always a lock

Genetic evidence is widely viewed as ironclad. In 'cold hit' cases, however, the truth is often elusive.

For more than three decades, Sylvester's slaying went unsolved. Then, in 2004, a search of California's DNA database of criminal offenders yielded an apparent breakthrough: Badly deteriorated DNA from the assailant's sperm was linked to John Puckett, an obese, wheelchair-bound 70-year-old with a history of rape.

The DNA "match" was based on fewer than half of the genetic markers typically used to connect someone to a crime, and there was no other physical evidence.

...

Puckett insisted he was innocent, saying that although DNA at the crime scene happened to match his, it belonged to someone else.

At Puckett's trial earlier this year, the prosecutor told the jury that the chance of such a coincidence was 1 in 1.1 million.

...

Prosecutors and crime labs across the country routinely use numbers that exaggerate the significance of DNA matches in "cold hit" cases, in which a suspect is identified through a database search.

Jurors are often told that the odds of a coincidental match are hundreds of thousands of times more remote than they actually are, according to a review of scientific literature and interviews with leading authorities in the field.

Two national scientific committees, including the FBI's DNA advisory board, have recommended portraying the odds more conservatively. But interviews with expert witnesses and DNA analysts from crime labs across the country show that few if any have adopted that approach.

...

DNA profiles are widely perceived as a unique genetic fingerprint. In fact, they are slivers of the human genome -- up to 13 markers that contain about a millionth of the information on all the chromosomes. Relatives often share many markers, and even unrelated people on average share two or three.

So DNA "matches" by themselves can never definitively link someone to a crime.

The best science can do is to estimate the likelihood that a match has occurred by sheer chance. These statistics are easily distorted or misunderstood by lawyers, judges, juries and even expert witnesses.

LA Times

[LiberalFighter]

8. The odds are determined on what they have in their database.

Their database does not have the dna of everyone.

Their database consists mostly of those that have been convicted, suspects or other required collections.

In 2006, Britain was determined to have the largest DNA database consisting of 4.25 million people. That is just over 7% of the population.