The family of Joshua Brown, a witness in the murder trial of a Dallas police officer, asked for an independent investigation into his fatal shooting while the manhunt continued Wednesday for a third suspect in the case.

Dallas police announced Tuesday that two suspects in Brown's death were in custody and a third was being sought.

"I’m glad that (Dallas police) believe they have the suspects in the Brown killing identified," said S. Lee Merritt, a lawyer for Brown's family. "All I ask is that they have another law enforcement agency take over to make sure all the bases are covered due to the circumstances in this case."

Brown was a witness in the trial of former police officer Amber Guyger, who was convicted last week of killing a neighbor, Botham Jean, in his apartment after mistaking it for her own and him for an intruder. Brown's testimony was crucial because he lived on the same floor as Guyger and heard them talking but did not hear Guyger shout verbal commands or warnings before shooting Jean.

How many years will Amber Guyger stay in prison? That could depend on Botham Jean's family

Brown was found shot to death in a parking lot Friday, two days after Guyger was sentenced to 10 years in prison. Dallas Deputy Police Chief Avery Moore said Tuesday that Brown was killed in a drug deal that devolved into a gunbattle.

Authorities confiscated 12 pounds of marijuana, other drugs and $4,000 in cash from Brown's apartment.

Michael Mitchell, 32, was arrested by federal deputy marshals Tuesday night in Marksville, Louisiana. His nephew Jacquerious Mitchell, 20, was in critical condition in a Dallas hospital with a gunshot wound.

A manhunt was underway for Thaddeous Green, 22.

Before details of the slaying were announced, the NAACP Legal Defense and Education Fund and others called for an independent investigation into Brown's death and the Dallas Police Department.

Moore chastised those who implied that police were somehow linked to Brown's death.

“I assure you that is simply not true," Moore said. "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.”

Tensions between Dallas police and community activists erupted into shouting and shoving Tuesday at the first meeting of a new Community Police Oversight Committee.

Contributing: The Associated Press