The recent U.S. Supreme Court decision to allow police to continue collecting DNA samples when arresting violent offenders supports use of a powerful investigative tool, a law enforcement spokeswoman said.
"DNA is a tool like no other tool law enforcement has ever had," said Kristin Helm, with the Tennessee Bureau of Investigation. "It is better than a fingerprint, better than a photograph. It's just instrumental in making sure that you have the right person."
Twenty-eight states have practiced this collection method for years. How the samples are stored, accessed or used for investigations varies by state.
DNA is commonly collected with a cotton swab rubbed along the inside a of a person's cheek; a blood sample is not required.
Since 2008, Tennessee has allowed DNA collection without a warrant when a suspect is arrested on a violent offense. The TBI maintains a database of those samples that investigators can request to have searched to see if samples they have on active criminal cases match any others in the system.
DNA evidence helped rule out suspects in two high-profile cases that local defense attorney Lee Davis handled when he worked as a prosecutor for the Hamilton County District Attorney's Office in the 1990s.
One case involved the rape and murder of a 4-year-old girl on Sept. 30, 1994. Two men, Paul Crum and Paul Ware, were at the 414 Stringer St. home at the time of Lindsay Green's death.
Hairs found in Green's body were tested for mitochondrial DNA and matched just one of the men -- Paul Ware.
He was convicted of first-degree murder and sentenced to life without parole.
Another case involved what appeared to be a serial rapist that Chattanooga police Sgt. Bill Phillips investigated.
Between January 1995 and July 1996 police got five rape or attempted rape reports from the East Brainerd and East Lake areas.
Phillips was assigned to some of the early cases and started noticing patterns in the rapist's methods.
But until he had a name and more information he didn't have anywhere to go.
Then he nailed down a name through his interviews -- Michael Anderson Peek. Phillips got a judge to sign a warrant so he could get Anderson's DNA sample.
He didn't have enough to arrest the man, but hoped Peek might say something damning when they talked.
Peek said he didn't know anything.
Phillips picked up the phone and got the crime lab to rush tests on one of the five cases that they'd gotten DNA evidence.
The phone rang. A lab technician told Phillips, "Hey, that's your guy."
That was enough to arrest and hold Peek on bond while results came back from the rest of the tests.
In 1997, a jury convicted Peek on all five cases and Hamilton County Criminal Court Judge Doug Meyer sentenced him to 99 years.
Phillips said DNA is only part of the investigative process, as the Peek case showed. Good police work builds the case, he said.
"It's not something you want to abuse," Phillips said.
Helm said one technician handles all of the test requests for the state, Helm said.
Police have submitted 80,000 DNA samples to TBI since 2008, she said. Of those, 60,000 are people who've been convicted and whose samples are stored for future investigations. The rest are being analyzed.
Until there is a conviction, the samples are not permanently stored. And if a person is acquitted or exonerated the sample is destroyed, Helm said.
In the past four years there have been 693 "hits" or matches to DNA in the system and cases being investigated.
The Tennessee database is connected to the FBI nationwide database. Other states can request to see if there are DNA matches in their cases.
Davis, now a private defense attorney, stressed that using DNA in criminal cases benefits both sides.
"That's why it's a powerful tool," Davis said. "It's not a defense attorney tool or a prosecutor's tool. It's an evidence tool."
He compared current-day concerns about DNA sampling to worries about fingerprinting. When fingerprinting was first used by police to solve crimes, many people saw the practice as an impossible science and questioned privacy concerns. Today, fingerprinting is commonly accepted.
In his decades-long legal career, Davis said he's seen attitudes on DNA shift, from a reputation as a "spooky science" when it first came into the courts to an accepted, reliable tool.
Contact staff writer Todd South at email@example.com or 423-757-6347. Follow him on Twitter @tsouthCTFP.