Investigator Explains How DNA Sealed Bennett Murder Case

She was not directly involved in the Stephanie Bennett murder case, but as a forensic biologist within the State Bureau of Investigation's Crime Laboratory, she knows what it takes to solve difficult cold cases involving DNA evidence.

Here's how it works: DNA is extracted from a sample and then amplified to make the sample larger before a genetic profile is generated, Fox said.

DNA is so unique that only identical twins have the same makeup, she said.

In the Bennett murder case, police said there was a solid match with DNA found in Bennett's apartment on the night she was killed three years ago to Drew Planten, who was charged Wednesday in her death.

In this case and others, Fox said a DNA match means there is no chance police can arrest the wrong suspect.

"The statistical values we generate are a billion to million, a million to trillion, thousand to trillion. Those types of numbers," Fox said. "So it's more likely to be that person than the world's population. Therefore, we feel pretty confident when we get a match."

According to investigators, Planten did not voluntarily submit a DNA sample. Police were able to get one of their own, though they would not say how.

"Occasionally, we'll get samples from cigarette butts, glasses that someone has drank from," Fox said. "We can get soda cans or anything that has come in contact with the body."

And though the technology to match DNA samples has been available for only about a decade, it has already helped solve hundreds of cold cases.

So far this year, the SBI has worked on more than 1,100 cases, and two thirds of those cases have been solved, in large part due to DNA samples. DNA matches also have led to more than 150 arrests in cold cases this year. There were 64 arrests for cold cases in 2004.

"It's so gratifying," Jerry Richardson, director of the SBI Crime Lab, said. "I can't even express it in words."