An attorney for alleged serial killer Kenneth Gleason on Friday challenged DNA results that prosecutors say linked him to the 2017 slaying of a Black homeless man at a Baton Rouge bus stop.

Lawyer Jarrett Ambeau said during Gleason's first-degree murder trial that only a trace amount of touch DNA was found on shell casings recovered from the scene of Bruce Cofield's killing.

Louisiana State Police Crime Lab DNA analyst Ashley Malone, a prosecution witness, acknowledged under questioning by Ambeau that the amount of DNA found on the shell casings was low.

Ambeau characterized the amount of DNA material as "a very low level."

But Malone later told prosecutor Dana Cummings the DNA collected from the shell casings was "not an extremely low level."

Ambeau continued to hammer away at the DNA evidence with Malone on the witness stand, saying, "This is a science experiment, at the end of the day. There's a lot of uncertainty in this process."

Malone defended the validity of DNA evidence, noting the State Police Crime Lab has also used it to exclude suspects in criminal cases.

"It is a reliable science," she testified.

Gleason, 27, who is White, is standing trial only in the Sept. 14, 2017, shooting death of Donald Smart, a 49-year-old Black man, on Alaska Street just north of the LSU campus.

But evidence from the fatal Sept. 12, 2017, shooting of Cofield near the intersection of South Acadian Thruway and Florida Boulevard, as well as a Sept. 11, 2017, nonfatal shooting in the Hickory Ridge subdivision off Coursey Boulevard, is also being introduced at the trial.

Gleason faces a mandatory life sentence if found guilty as charged in Smart's death. The verdict must be unanimous. The trial will enter its third week Monday. 

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Gleason faces a second-degree murder charge in the slaying of Cofield, 59, and two counts of attempted second-degree murder in the non-fatal shooting in which he's accused of firing three shots into the home of a Black family on his street, Sandy Ridge Drive.

Prosecutors have said Gleason is linked to Cofield's killing and the non-fatal shooting through DNA evidence, and to both deadly shootings and the nonfatal incident through ballistics evidence.

Ambeau also suggested Friday that there was "possible contamination" involving a DNA sample taken from Gleason, the shell casings from the Cofield homicide scene and a pair of tennis shoes seized from Gleason's home because of the way the State Police Crime Lab handled those items.

But Malone testified she has no reason to believe contamination occurred in the case.

"We have a lot of quality controls and procedures," she assured.

Smart was gunned down as he walked to his overnight shift at Louie's Cafè, where he worked as a dishwasher. Prosecutors decided against seeking the death penalty after consulting with his family.

Twenty-six 9mm shell casings were recovered from the scenes of the three nighttime shootings, according to police. Authorities determined they were fired from the same unknown gun.

Gleason purchased a CZ 9mm gun with a 15-round magazine in November 2016 and applied for a silencer on July 20, 2017, less than two months before the shootings began, according to prior trial testimony.

Authorities have said the shootings were apparently random and possibly racially motivated. An FBI agent testified Wednesday that Gleason searched the internet between Sept. 1 and Sept. 16, 2017, for topics such as White nationalism, genocide, Nazi propaganda and gun silencers.

Gleason's lawyers have said he studied German at LSU. He attended the university for one year starting in the fall of 2012.

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