Dallas police have identified three suspects linked to the case of a slain witness who testified in the murder trial of former Dallas police officer Amber Guyger. Authorities say two suspects are in custody, and one other is being sought on capital murder charges in the death of Joshua Brown, police said Tuesday.

Brown was killed in a drug deal gone bad, police announced, and they emphasized his death was not related to his testimony in the Guyger case.

The 28-year-old was a key prosecution witness in the trial of Guyger, who was convicted last week in the 2018 killing of her neighbor, Botham Jean. Brown lived across the hall from Jean and testified that he heard two people "meeting by surprise," followed by two shots, the night Jean died.

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Brown was shot to death at a separate apartment complex Friday, just 10 days after taking the stand.

In this September 24, 2019, photo, Joshua Brown, left, answers questions from Assistant District Attorney LaQuita Long, right, while pointing to a map of the South Side Flats where he lives, while testifying during the murder trial of former Dallas Police Officer Amber Guyger. AP

Dallas Police Assistant Chief Avery Moore said the three suspects had traveled from Louisiana to buy drugs from Brown, and one of the men shot Brown twice and killed him.

One of the suspects, 20-year-old Jacquerious Mitchell, was wounded and treated at a hospital. He's expected to be charged with capital murder. Police are still searching for Thaddeous Charles Green, 22. Late Tuesday, Michael Diaz Mitchell, 32, was in the custody of Avoyelles Parish Sheriff's Office after he was handed over by the U.S. Marshall's Violent Offender Task Force.

Through the dedicated work of the DPD homicide detectives, we have identified 3 suspects in the murder of Joshua Brown. Jacquerious Mitchell B/M age 20, Michael Mitchell B/M age 32 and Thaddeous Green B/M age 22 pic.twitter.com/v0vikYEpD4 — Dallas Police Dept (@DallasPD) October 8, 2019

Jacquerious Mitchell told police it was Green who contacted Brown to buy the drugs, according to police. Mitchell said Green and Brown were talking when the conversation escalated into a physical confrontation. During the dispute, Brown shot Jacquerious Mitchell and Green shot Brown, killing him, according to Jacquerious Mitchell's account. Mitchell said he was driven to a hospital before the other two suspects fled.

Dallas Police said "numerous tips" led them to search Brown's apartment, where they confiscated 12 pounds of marijuana, 149 grams of THC cartridges and more than $4,000 in cash.

Brown was concerned for his safety and didn't want to testify in the Guyger trial because he believed he had been targeted in a previous November 2018 shooting, according to his family lawyer, Lee Merritt. The shooting at a Dallas strip club last year left Brown wounded and killed Nicholas Shaquan Diggs, reports CBS Dallas/Fort Worth.

Brown was also expected to testify in an upcoming trial in Diggs' death, the station reports.

Merritt told CBS DFW that the day Brown testified, someone posted on one of Brown's social media accounts, "Now we know where to find you." The post was later deleted.

Merritt and others have called for an outside agency to investigate Brown's death. Dallas Police did not immediately respond to a request for a response from CBS News.