Three Louisiana men are suspected 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 or case.

The suspects — Jacquerious Mitchell, 20; Michael Mitchell, 32; and Thaddeous Green, 22 — are from Alexandria, Louisiana, and investigators believe they were in Dallas to buy drugs from Joshua Brown , Assistant Chief Avery Moore said at a news conference.

Moore said Jacquerious Mitchell told police that Brown shot him in the chest after Green and Brown began fighting during the drug deal, and that Green then shot Brown twice.

Jacquerious Mitchell is in a Dallas hospital in “critical condition,” police said. Neither Michael Mitchell, who is Jacquerious’ uncle, nor Thaddeous Green are in custody.

Green left with Brown’s backpack and gun, police said.

Authorities confiscated 12 pounds (5.4 kilograms) of marijuana, 149 grams of THC cartridges and more than $4,000 in cash during a search of Brown’s home.

Brown’s death Friday came two days after a jury sentenced former police Officer Amber Guyger to 10 years in prison for killing her upstairs neighbor, Botham Jean. Guyger killed Jean in September 2018 in his fourth-floor apartment, which she said she mistook for her own unit one floor below.

Brown, who lived on the same floor as Jean, testified that on the night Jean was killed, he heard what sounded like “two people meeting by surprise” and then two gunshots. He said he had met Jean, a 26-year-old accountant from the Caribbean island nation of St. Lucia, for the first time earlier that day.

An attorney for Brown’s family previously said Brown had had reservations about testifying in such a high-profile trial because he had been wounded in a shooting outside of a Dallas strip club last year. Police Major Max Geron said Tuesday that investigators have no evidence linking that shooting to Brown’s death.

Dallas’ mayor and other officials had asked the public to refrain from speculating about the circumstances surrounding Brown’s killing while police investigated. Moore addressed that Tuesday.

“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 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.”

The NAACP Legal Defense and Educational Fund Inc. had requested an independent investigation into Brown’s death, calling it “deeply alarming and highly suspicious” in a news release.

(AP)