Joshua Brown, the Dallas man who was murdered after taking the stand in Amber Guyger’s trial, was gunned down in a drug deal — and the slaying had nothing to do with the killer cop’s case, a police official said Tuesday.

Jacquerious Mitchell, 20, Michael Mitchell, 32 and Thaddeus Green, 22, all came from Louisiana to buy drugs from Joshua Brown on Friday, Chief Avery Moore of the Dallas Police Department’s Criminal Investigation Unit said at a Tuesday press conference.

When they got there, Green got out of the car to speak with Brown — and the two had an argument that turned physical, Moore said.

Then, Jacquerious got out of the car — prompting Brown to order him back inside and shoot him in the chest, according to Moore.

The wounded Mitchell told police that he then heard Green popping off two rounds at Brown, according to Moore.

An autopsy report reveals that one of the bullets entered just below Brown’s spine and traveled upward, piercing vital organs, according to the police official.

Green grabbed Brown’s backpack and gun, and then hopped back into the car, driven by the older Michael, Moore said.

Michael dropped Green off at an unknown location before bringing Jacquerious to the hospital, according to Moore.

Jacquerious was moved to a different hospital, where he remains in police custody, and authorities are set to execute a capital murder warrant on him later Tuesday, Moore said.

Capital murder warrants have also been issued for the other two suspects, who remain at large, according to Moore.

Meanwhile, authorities executed a search warrant at Brown’s apartment, finding 12 pounds of marijuana, 143 grams of THC cartridges and $4,000, according to Moore.

Moore shot down any suspicions that the slaying was connected to the Guyger case.

“As you know, there’s been speculation and rumors that [have] been shared by community leaders claiming that Mr. Brown’s death was related to the Amber Guyger trial, and somehow the Dallas Police Department is responsible,” he said. “I assure you that is simply not true, and I encourage those leaders to be mindful of their actions moving forward, because their words have jeopardized the integrity of the city of Dallas as well as the Dallas Police Department.”

Brown previously fled to California after repeatedly expressing concerns that testifying in the Guyger trial would put his life at risk, according to Lee Meritt, who represents the Jean family.

He returned at the behest of prosecutors.

Guyger, 31, was convicted last week in Jean’s murder and sentenced to 10 years behind bars.