One New York judge ruled the DNA evidence was scientifically sound. Another, just miles away, tossed it out as unreliable.

The same scenario is playing out in courthouses around the world amid a debate over whether a type of DNA analysis involving the amplification of tiny amounts of genetic material is reliable enough to convict someone for a crime.

The technique, known as low-copy number or high-sensitivity analysis can be used when investigators use "touch DNA" and are only able to collect a few human cells left behind when someone touches an object such as a gun, the handle of a knife, or even clothing.

While many prosecutors and forensic experts hail it as powerful tool that can help close cases, critics — most notably the FBI — argue it is inconclusive and unreliable. But there is no clear case law on the merits of the science, leaving judges to evaluate it on a case-by-case basis.

"If the experts in the DNA field cannot agree on the weight to be given to evidence produced by high sensitivity analysis, it would make no sense to throw such evidence before a lay jury," Brooklyn state Supreme Court Justice Mark Dwyer said last year in throwing out a DNA sample swabbed from a bicycle in an attempted murder case.

With low-copy number DNA, the samples are so small — less than 100 picograms, or about 16 human cells — that scientists amplify them more than typical DNA samples and that's one of the reasons critics say the technique is troubling.

"It's more likely to pick up contamination, transference," said Jessica Goldthwaite, a staff attorney with the Legal Aid Society's DNA unit, who worked on the Brooklyn case. "You can't be assured of the reliability of the results."

For example, she said, "you shake my hand and then I touch a gun, your DNA could end up on the gun."

Such concerns prompted the FBI to forbid laboratories to run low-copy number profiles through the national DNA database. The FBI has said it is studying the use of low-copy DNA analysis but it hasn't "demonstrated the necessary reliability for use in forensic casework."

Perhaps the most high-profile example of the technique, and the controversy, came in the case of Amanda Knox, the American college student charged with killing her roommate in Italy. A low-copy number DNA sample taken from the handle of a kitchen knife helped convict her but a forensic report in 2011 called the evidence unreliable and possibly contaminated, leading to the exoneration of both Knox and her co-defendant. The two were later retried, convicted and exonerated a second time.

The technique was also used in New York in a weapons possession case involving entertainer Lil Wayne. A judge ordered a hearing after prosecutors tried to use the technique to tie him to a gun found on his tour bus in 2007. The rapper eventually pleaded guilty in the case.

Notably, New York stands out for its aggressive use of the technique.

New York City's medical examiner's office says it uses the protocol in about 10 percent of the DNA cases it analyzes. Its forensic scientists have performed about 7,500 low-copy number tests since 2005 and have testified in close to 250 cases in state and federal court.

"?Removing it as a tool for police and prosecutors would lead to significant setbacks in 21st century evidence-gathering techniques," said Emily Tuttle, a spokeswoman for Manhattan District Attorney Cyrus Vance, Jr.

Just this past week, a former director of the city's medical examiner's office filed a federal civil rights lawsuit alleging that she was forced out of her job after questioning its use of low-copy DNA testing.

Dr. Marina Stajic, who also served on a state commission tasked with developing standards for DNA labs, claimed she was ousted when she voted to require the medical examiner's office to publicly release a study about the testing technique.

Julie Bolcer, a spokeswoman for New York City's medical examiner's office, declined to comment specifically on Stajic's claim, citing ongoing litigation, but said the office is dedicated to using "the most accurate and advanced technology."

"Low copy number DNA testing provides a tool for solving cases that is recognized as reliable and generally accepted by the scientific community," she said.


Follow Michael Balsamo on Twitter at His work can be found at