Ted Kergan’s relentless pursuit of justice for his slain brother, Gary, a Crowley businessman last seen alive more than three decades ago in Baton Rouge, moves into its next — and perhaps final — phase Tuesday when a 66-year-old Bossier City man goes on trial in the 1984 killing.

Ronald Dalton Dunnagan, described in the mid-1980s as a drifter, is charged with second-degree murder and would spend the rest of his life behind bars if found guilty as charged.

Dunnagan has been arrested three times in the case.

His alleged accomplice, former exotic dancer-turned-nurse Leila Mulla, pleaded guilty last year to manslaughter and was sentenced to 30 years in prison.

She is expected to be the star prosecution witness at Dunnagan’s trial. Jury selection is set to begin Tuesday at the 19th Judicial District Courthouse in downtown Baton Rouge. State District Judge Mike Erwin will preside over the trial.

“My family has waited 31 years and never given up on seeking justice for Gary’s killers,” Ted Kergan, who was his brother’s business partner, said last week. “I only wish my mother were alive to witness this trial. She died not knowing what happened to her son.

“My family rested easier after Leila Mulla confessed her role in the murder. We’re ready for the next step in seeking justice for Gary.”

A major step in that quest came in May 2014 when Mulla, 50, of Astoria, New York, implicated Dunnagan in Gary Kergan’s death. She admitted in court that she gave the 34-year-old Kergan wine allegedly poisoned by Dunnagan in a plot to rob and kill him.

Dunnagan was indicted in September 2014 and is represented by the local public defender’s office.

Kergan, whose body was never found, was declared legally dead by the courts in 1986.

A substantial amount of blood was discovered in the trunk of Kergan’s car when the abandoned Cadillac El Dorado was found on Severn Avenue in Metairie several days after his Nov. 29, 1984, disappearance. In 2012, DNA testing not available at the time of the crime showed the blood was Gary Kergan’s.

Mulla, who danced at the Night Spot Lounge on Plank Road, admitted leaving the lounge with Kergan and luring him to her Byron Street apartment in north Baton Rouge, where Dunnagan was allegedly hiding. Mulla and Dunnagan shared the apartment, police have said.

East Baton Rouge Parish Assistant District Attorney Dana Cummings said last year in court that Dunnagan dragged Kergan into another room after he was poisoned “to complete the murder.” The prosecutor said Dunnagan placed the body in the trunk of Kergan’s car to get rid of it.

Kergan had roughly $2,000 in cash in his possession and jewelry worth more than $8,000 on the night he vanished, police have said.

Court records state Dunnagan was Mulla’s boyfriend, but her attorney said last year that she was a teen runaway and a victim of human trafficking at the hands of Dunnagan. The attorney, Frank Holthaus, said Dunnagan prostituted Mulla and other girls for money. Mulla received none of the money, Holthaus added.

Dunnagan and Mulla were arrested for the first time in Las Vegas in December 1984 and accused of conspiring to rob Kergan. They were set free the next spring after then-East Baton Rouge Parish District Attorney Bryan Bush declined to prosecute them. He cited a lack of evidence.

They were arrested again in December 2012 after DNA testing confirmed the blood found in the trunk of Gary Kergan’s car belonged to Kergan.

Mulla was indicted in 2013, but an East Baton Rouge Parish grand jury took no action against Dunnagan. He was released from jail. Mulla was not cooperating with authorities at the time.

Dunnagan was arrested a third time after his 2014 indictment.

The Kergan brothers owned a chain of Sonic Drive-In restaurants in south Louisiana.