(CNN) -- Joshua Brown, a key witness in the murder trial of a former Dallas police officer convicted of the shooting their neighbor in his own apartment, was shot and killed during a drug deal gone wrong, Assistant Chief Avery Moore said.
Brown was killed after an argument with one of three men from Louisiana who had met him in Dallas for a drug purchase, Moore told reporters.
A conversation between Brown and Thaddeus Green, 22, escalated into a physical altercation in which Brown allegedly shot and wounded Jacquerious Mitchell, 20, according to Moore. Green then shot Brown twice, police said. Green took a backpack from Brown as well as the gun used to wound Mitchell.
After receiving tips, police obtained a search warrant and recovered 12 pounds of marijuana, 143 grams of THC cartridges, and $4,000 in cash from Brown's apartment.
"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 was responsible," Moore 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."
Police have obtained arrests warrants for the three men, including Michael Diaz Mitchell, 32, who was driving the car, Moore said. Only Mitchell is in custody. He's expected to be charged with capital murder.
Brown, 28, was fatally shot Friday at his home in the Atera Apartments, about five miles from his former complex where he, former officer Amber Guyger and their neighbor Botham Jean lived.
Brown teared up as he testified last month in Guyger's murder trial.
After Brown was killed Friday, witnesses told police they saw a silver, four-door sedan speed from the parking lot after the shooting, and police had asked the public to come forward with information on the case.
Almost a year before he testified at Guyger's trial, Brown was wounded in a shooting at a Dallas strip club that left another man dead, police said.
Brown believed he was the target in that November 23 shooting and felt there were "still people out there who wanted to do him harm," said attorney S. Lee Merritt, who represents Brown's family.
Merritt on Tuesday called for Dallas police to recuse themselves from the investigation into Brown's shooting.
Several presidential hopefuls have urged authorities to solve the case. Merritt has called for an independent investigation into the killing, acknowledging that speculation has begun to spread. He said it "doesn't mean there's evidence" of police involvement or connection to the Guyger case.
The NAACP Legal Defense and Educational Fund, Inc. (LDF) also requested an investigation into Brown's death.
Jean was shot and killed by Guyger on September 6, 2018. On November 23, Brown was shot at a strip club, Dallas Cabaret South, according to a police blotter item. A full police report on that shooting was not immediately available.
Citing an affidavit, the Dallas Morning News reported that a man had waited for Brown outside the club and the two fought. The man started shooting when Brown tried to leave, wounding his foot, the newspaper reported. Nicholas Shaq'uan Diggs, 26, was killed.