An Orleans Parish jury convicted a 20-year-old Harvey man early Tuesday morning in the high-profile murder of Harry “Mike” Ainsworth, an Algiers Point man who was killed trying to halt a neighbor’s carjacking nearly three years ago as his two young sons looked on.

The jury deliberated for more than six hours before finding Kendall Harrison guilty as charged of second-degree murder and armed robbery with a firearm, in what became known as the “Good Samaritan” case.

The verdict came down at 3:10 a.m., ending a Criminal District Court trial that ran into its eighth day.

The drawn-out trial was marked by frequent testy exchanges between prosecutors with District Attorney Leon Cannizzaro’s office and defense attorney Lionel “Lon” Burns, a former prosecutor who this year ran a brief campaign to unseat Cannizzaro before the Louisiana Supreme Court disqualified him over tax issues.

In his closing argument Monday evening, Burns lambasted a police investigation led by a homicide detective who was heading up her first case as lead investigator. Burns told the jury of six men and six women that police planted Harrison’s DNA — the central evidence in a case with no clear eyewitness identification, no murder weapon and no confession from Harrison to police.

Earlier Monday, an expert testified that material swabbed from the steering wheel of Anita Hedgepeth’s car following the Jan. 25, 2012, carjacking attempt and shooting turned up a “trace” DNA match to Harrison.

Burns suggested that police, frustrated at failing to solve a murder case that shook the city, took a shortcut to incriminating Harrison, whose name had been raised in tips to police.

“I contend that the DNA of Kendall Harrison was placed in this case. Reach your own conclusion. Was it added to the car? Were the swabs tampered with?” Burns said to the jury.

Burns was aiming to exploit an admission by Detective Tanisha Sykes that she had failed to adhere to NOPD policy by neglecting to get two witnesses to sign photo lineups in which they fingered a “filler” photo, failing to identify Harrison.

“That’s the problem with this case. Nobody can make a reliable identification,” Burns told the jury. “Being the detective she is, she was going to make something happen. She was going to make something out of nothing. The whole police force was watching her.”

Assistant District Attorney Payal Patel fired back, calling the theory “disingenuous, cheap and dirty.” She noted that the DNA swab from the steering wheel was logged into the State Police lab in Baton Rouge well before police came calling for Harrison’s DNA on Feb. 6, 2013, 12 days after the killing.

At one point during their deliberations, the jury asked to view the DNA packages sent to the lab.

Harrison did not testify in the case.

Among the witnesses, however, was a convicted armed robber, Joshua McReynolds, who testified that, while housed in Orleans Parish Prison, Harrison admitted killing Ainsworth during the failed carjacking attempt.

“He said he didn’t want to kill the guy. He just got in his way. He was scared,” McReynolds told the jury. “I asked him what’s it like to kill a guy. He said it was similar to shooting a bird with a BB gun.”

Judge Darryl Derbigny began instructing the jury shortly after 8 p.m.

Patel and fellow prosecutor Alex Calenda laid out an array of evidence, including testimony from a cousin and aunt of Harrison who placed him three blocks from the scene within a half-hour of the killing in the 500 block of Vallette Street.

Harrison had told detectives he was in Harvey at the time and hadn’t been in Algiers Point for more than a week before Ainsworth, 44, was shot twice in the chest through the windshield of Hedgepeth’s Saturn Ion.

Ainsworth heard screams and ran from the bus stop where he’d dropped off his two boys, ages 9 and 10, at 7 a.m. He leaped onto the Saturn’s windshield and bashed it with his arms and fists before the carjacker fired a 9mm weapon through the windshield, according to testimony.

Early in the trial, Burns portrayed Ainsworth as an overzealous vigilante, while highlighting a toxicology report that showed he tested positive for marijuana in his system.

Patel described Burns’ defense as nothing but “whoopin’ and hollerin’ ” as she wrapped up more than three hours of closing arguments.

“I think you’ve seen their desperation and their last-minute grasping of their last hope,” she said. “What do you do in the face of irrefutable evidence? The defense team has decided to attack the Ainsworth family. They’re grasping at straws.”

Patel cited testimony about the careful transport of the DNA evidence to the State Police lab. For the jurors to believe that Sykes planted DNA evidence, Patel told them, “You’d also have to believe in time travel.”

Harrison’s father, Michael Willis, took the witness stand Monday to vouch for his son, saying Harrison, who was 17 when Ainsworth was killed, never owned a gun. That opened the door for prosecutors to show the jury a photo taken from Harrison’s cellphone that showed him carrying a gun that Calenda said likely was the murder weapon.

Prosecutors rebuffed Burns’ suggestion that Ainsworth, a member of a New Orleans police booster group, invited his own death.

“I’ll tell you right now, Mike Ainsworth is a hero. Mike Ainsworth gave his life to protect a person he didn’t even know,” Calenda told the jury.

Harrison, who was arrested about a month after Ainsworth’s killing, faces a life prison term.

Follow John Simerman on Twitter, @johnsimerman.