Three men will face murder charges in connection with the deadly shooting of a witness who testified in the murder trial of ex-Dallas police officer Amber Guyger, police say.

Joshua Brown, 28, was shot twice in his lower body Friday night during a drug deal in the parking lot of the Atera apartments on Cedar Springs Road, near the Dallas North Tollway and Lemmon Avenue. He died later that night at Parkland Memorial Hospital.

In a news conference Tuesday afternoon, Dallas police investigators said they believe the suspects traveled approximately 300 miles — a 4 1/2 hour's drive — to buy marijuana from Brown.

Dallas County Sheriff's Office

Thaddeous Green, 22, remains at large Wednesday. He is considered by police to be armed and dangerous. Dallas police detectives are in Louisiana searching for the remaining fugitive and are working with federal partners, officials said.

Dallas police said in a statement late Tuesday that 32-year-old Michael Mitchell was taken into custody at a motel in Marksville, Louisiana. The third suspect, Mitchell's nephew, 20-year-old Jacquerious Mitchell, was in critical condition in a Dallas hospital following an exchange of gunfire with Brown.

Later Tuesday, Avoyelles Parish sheriff's deputies said Michael Mitchell was taken into custody without incident and faces charges of possession with intent to distribute, convicted felon in possession of a firearm and illegally carrying a weapon.

One man is in custody and two others are wanted in connection with the deadly shooting of the man who testified in the Amber Guyger murder trial.

Anyone with information that can help locate Green is asked to call police at 214-373-8477 or 214-671-3690.

Brown's shooting received national attention after igniting speculation on social media and prompting calls for an independent investigation into whether the shooting was related to the trial, which ended in a guilty verdict just days before.

DPD says the killing was not tied in any way to Brown's testimony and criticized "community leaders" for undermining their investigation.

"The rumors shared by community leaders that Mr. Brown's death was related to the Amber Guyger trial and that DPD was responsible are false. We encourage those leaders to be mindful because their words may jeopardize the integrity of the city of Dallas and DPD," read a tweet sent on the official Dallas Police Department Twitter page moments after Tuesday's news conference.

Dallas' mayor has asked the public to avoid speculating about the fatal shooting of a witness in the recent trial of former police officer Amber Guyger, who was convicted of murder in the killing of her upstairs neighbor, Botham Jean.

Brown, who was a neighbor of Botham Jean's at the South Side Flats apartments, had testified about hearing gunshots the night Jean was shot and killed by Guyger. She was later found guilty of murder and sentenced to 10 years in prison.

An attorney representing Brown's family previously said Brown had had reservations about testifying in such a high-profile trial because he had been wounded in a separate shooting last year.

Police said Brown's shooting death was not related to the incident in which he was shot last year.

Merritt, who initially spread a false report that Brown was shot in the mouth, offered no apologies.

"I am not implicating the Dallas Police Department," he said. "They're already implicated by virtue of this high-profile trial. They already lost credibility."

Dallas Mayor Eric Johnson also weighed in via Twitter.

Three Louisiana men are wanted in the killing of a witness who testified at the murder trial of a former Dallas police officer, authorities said Tuesday, cautioning that the killing had nothing at all to do with that trial and case.

"I am grateful that our detectives have taken the initial steps necessary to bring closure to this case," he said. "I want to thank everyone who demonstrated patience and responsibly reserved their judgment while the Dallas Police Department gathered the facts regarding the death of Joshua Brown. I urge anyone with additional information about this case to come forward."

NBC 5's Scott Gordon, Maria Guerrero and Chris Blake contributed to this report.