A second suspect has been arrested in connection with the killing of Joshua Brown, a key witness in the Amber Guyger murder trial.

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Police claim that Brown was involved in a drug deal gone wrong, despite reports that he was targeted for helping the prosecution convict Guyger for the murder of Botham Jean.

On Tuesday, a second man, Michael Mitchell, 32, was arrested, The Daily Mail reports. This follows the arrest of 20-year-old Jacquerious Mitchell, 20 who is in is critical from a gunshot wound.

Police Chief Avery Moore said those two suspects, along with Thaddeous Green, 22, are drove from Alexandria, Louisiana, to Dallas to purchase drugs from Brown.

According to Mitchell, Green had contacted Brown for the purchase. But what he described as a “physical altercation” begins between Green and Brown.

As Jacquerious gets out of his vehicle, Brown shot him in the chest, he told officers. Once he fell into the vehicle, he said he heard two gunshots, which were of Green shooting Brown in the lower body.

Green then took Brown’s backpack and the gun he used to fire at Jacquerious and the three sped off, with Michael Mitchell as the getaway driver. Jacquerious was dropped off by the two at a local hospital where he remains in police custody and in critical condition. Dallas police later issued warrants for the arrest of all three, who now face capital murder charges. Green is still at large, police say.

Officials say 12 pounds of marijuana, 149 grams of THC cartridges, and about $4,000 in cash were found in Brown’s apartment in a search.

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The NAACP Legal Defense and Educational Fund is urging state and federal authorities to step in and launch an independent investigation into the killing of Joshua Brown, a key witness in the Amber Guyger trial.

“The circumstances surrounding the murder of Mr. Brown cries out for answers,” said Sherrilyn Ifill, president of the NAACP Legal Defense and Educational Fund in a statement on Sunday, The Dallas News reports. “Most importantly, it demands an independent investigation of how and why he was killed.”

Brown was slain Friday night outside his new apartment complex, about five miles away from where his then-neighbor Botham Jean was shot to death, according to various media reports.