(CNN) Three men were indicted by a grand jury on capital murder charges Thursday for allegedly killing Joshua Brown, a key witness in the murder trial of former Dallas police officer Amber Guyger, according to court documents.

Jacquerious Mitchell, Michael Mitchell and Thaddeous Green were indicted for the shooting death of Brown on October 4. The indictments say the three men attempted to rob him.

Previously, Dallas Assistant Chief of Police Avery Moore said Brown was killed after an argument escalated with Green in the parking lot of Brown's apartment complex. Brown allegedly shot and wounded Jacquerious Mitchell, according to Moore. Green then shot Brown twice and took a backpack from Brown and the gun used to wound Mitchell.

Brown's death came 10 days after he testified in the trial of Guyger, 31, who was convicted of murder for fatally shooting Botham Jean in his Dallas apartment in 2018. She argued that she mistakenly walked into the wrong apartment — she lived in the same building — and opened fire because she thought Jean was an intruder.

Guyger was sentenced to 10 years in prison.

Read More