When someones DNA triggers a match through a statewide database linking that person to the scene of a crime, it doesnt necessarily mean the case is a slam dunk for police and prosecutors.

Next comes the hard part: Investigators must prove there isnt an otherwise noncriminal explanation for why that persons genetic material was found on someones body, on a murder weapon or inside another persons home.

A lot of people think that if you get a DNA hit that, Bingo, you got the person, but it doesnt work that way, Oneida County District Attorney Scott McNamara said. What law enforcement needs to be cognizant of is that there are many innocent explanations for things to be where they are, and as we get better and better at being able to find DNA, we also have to keep in mind that there is an innocent way for DNA to be left behind.

Since New Yorks statewide database of DNA collected from convicted criminals has been expanded over the years, the ever-growing pool of samples to compare against has helped local police agencies crack tough cases, officials said.

For instance, DNA from a strand of hair found on Jennifer Bennetts body in 2007 ultimately linked Craig Ingersoll to her strangulation. Although Ingersoll never had been a suspect, a DNA match led investigators to question Ingersoll after Utica police arrested him in 2010 for stealing from a business and state law required him to provide a sample of his DNA.

This is great technology, but its not easy, Whitestown police Chief Donald Wolanin said. Knocking on doors and interviewing people is still one of our best tools and probably most reliable. Were arresting more people by doing basic police interviews than we are with DNA technology.

Here are a few examples of how complicated some cases can be, even with DNA evidence.

A bloody cloth

Utica police continue to investigate the killing of someone who was stabbed repeatedly. A bloody cloth recovered from the homicide scene did lead to a DNA match with a known person, but that individual has denied any involvement in the killing, prosecutors said.

DNA gives us a lead, but it doesnt give us enough to proceed, McNamara said. When we confronted the person with the bloody cloth, he said he didnt know what we were talking about. So, just because we find a bloody cloth with his DNA on it, that doesnt mean he killed anyone.

Excerpt from:
DNA not always the magic bullet in crime investigations