It's been almost three decades since a decomposed body was found in a culvert underneath a southern Arizona freeway.

Now, Marana police have identified the victim — a teenage girl from Spokane, Washington, who was fatally shot in 1987 after taking a bus trip to Arizona with a ticket possibly bought by her killer.

Police also believe they know who the murderer is. But he died in a Tucson prison in 2005, six years before being connected to the cold case.

"At least this gives the family some closure after all this time," said Sgt. Chris Warren, a spokesman for Marana police which announced Wednesday that DNA submitted by relatives for testing showed conclusively that the victim was Deanna Lee Criswell.

Police said Criswell would have been 16 years old when her body was discovered by a transient walking along Interstate 10 on Nov. 25, 1987.

Warren said advances in forensic science enabled authorities to identify Criswell's killer through DNA tests in November 2011 as William Ross Knight, a convict who died in a Tucson prison in 2005 while serving a life sentence for a series of armed robberies.

Knight was 48 when he died of end-stage liver disease.

Warren said investigators believe it's likely the lone murder case involving Knight, who was career criminal but only known for robberies.

"Someone in Tucson sent her a bus ticket. We think the killer did and they may have been in contact somehow," Warren said.

A handgun found in Knight's possession after his last arrest was the same caliber that the girl was shot with, according to Warren.

Although no witnesses ever surfaced, investigators believe Criswell may have been killed somewhere else about a week or two earlier and her body dumped in Marana.

The case was reopened in 2009. The victim's body was exhumed, the skull sent to Virginia for facial reconstruction and DNA testing was done.

But the case went cold again when authorities could not link the DNA to any samples in a national DNA database. However, information about the victim and case was posted to various social media sites.

A couple in Florida seeking information about their missing niece recently contacted Marana police about the unidentified victim.

Criswell finally was identified after DNA submitted by her parents and stepsister matched her DNA this week, according to police. The relatives' names weren't immediately released Wednesday.