When local attorney Joel Porter’s name surfaced last year in the cold-case investigation of his wife’s 1985 killing, he insisted he was innocent and sued a Baton Rouge police detective, claiming the officer defamed him by saying Porter had always been a suspect in the murder.

Now Porter contends that the discovery of an unknown person’s DNA on Denise Porter’s body proves he had nothing to do with her stabbing death.

Police say they can’t comment on his claims, citing the ongoing investigation.

A report about the DNA evidence, provided by Joel Porter to The Advocate, could signify that a yet-to-be-identified person killed his wife and left behind genetic material. It could also mean a crime scene worker inadvertently touched Denise Porter’s body without wearing protective gear.

Denise Porter, a 20-year-old former nursing student, was found stabbed to death inside her apartment on March 14, 1985. There were no signs of forced entry in the dwelling, and Joel Porter said he’d been at work all night before he came home to discover his wife dead.

A couple years ago, the Baton Rouge Police Department reopened Denise Porter’s case, including testing physical evidence with technology that wasn’t available when she was killed.

A report from the Louisiana State Police Crime Laboratory issued on April 29, 2014, which Joel Porter obtained from the Louisiana Attorney General’s Office in March, states that the ankle portion of Denise Porter’s gray sweatpants contains her DNA and that of an unknown person. The report ruled out Joel Porter as being connected to the DNA while also finding it isn’t linked to anyone in a nationwide criminal database.

According to investigative files, Denise Porter was apparently dragged by her ankles a short distance after she was stabbed. Authorities also believe her killer would have had to have left behind DNA somewhere in the apartment.

“The forensic testing results clearly exonerated me and proves that I was never implicated in my wife’s murder,” said Joel Porter, who has sued Baton Rouge Police Detective John Dauthier for writing in a search warrant, excerpts of which were subsequently published in The Advocate, that Porter “has always been a suspect” in the killing. No evidence has publicly surfaced that has directly linked Joel Porter to the crime.

Dauthier said though he’d “like to comment on the inaccuracy” of Joel Porter’s conclusion, he couldn’t speak about the matter because it’s an open investigation.

But Joanie Brocato, a forensic scientist and the DNA manager at the LSP Crime Laboratory, pointed out that very old evidence could contain DNA from any number of people working at a crime scene, muddling the process of closing in on a criminal.

“Any crime scene could have contamination from anyone present,” she said, while not addressing Porter’s case specifically. “That’s true even today as a possibility, but even more so of a case, let’s say, that’s 15, 20, 30 years old. If you take a case that’s that old, (there was) a total different mind frame when you entered a crime scene. You weren’t thinking about DNA.”

She added that investigators must be cautious when using “touch DNA,” the kind of material that was analyzed in this case. Touch DNA is an analysis of genetic material, such as skin cells, left behind by someone touching a surface. It’s less conclusive than using DNA from blood or semen, she said.

Joel Porter said BRPD has had some of the DNA evidence for two years and questions why it’s taken so long for the agency to test all the possible contributors and make progress with the case.

An attorney with the department declined to comment about those criticisms.

“The Baton Rouge Police Department does not comment on ongoing investigations,” Kim Brooks, a department legal adviser, said in an email. “Our department will not waver from its usual policy, despite the fact that Mr. Porter is determined to provide the media with constant commentary regarding this case.”

But Porter said he sees a more sinister motivation behind identifying him as a suspect and then not disclosing more information about the case.

“What has happened to me is no different than what is happening with black males across this country. The only difference, rather than shooting me in my back or gunning me down, (is) they took my reputation, my character and my name and they hung it from the highest tree in the most prominent, public place in the Baton Rouge city square,” Porter said of news reports of his being labeled a suspect in his wife’s murder. “It’s just a modern day, high-tech lynching of a black man.”

Follow Maya Lau on Twitter, @mayalau.