One of three suspects remained at large Wednesday in the death of Joshua Brown, a key witness in the murder trial of former officer Amber Guyger, who was convicted of killing a neighbor in his own apartment, Dallas police said.

Deputy Police Chief Avery Moore said Brown was killed in a drug deal that devolved into a gun battle. Brown was found shot to death in a parking lot Friday, two days after Guyger was sentenced to 10 years in prison for the September 2018 fatal shooting of Botham Jean. The accountant was eating ice cream in an apartment Guyger mistook for her own.

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

A manhunt was underway for Thaddeous Green, 22.

Moore said Jacquerious Mitchell told authorities he, his uncle and Green had gone to Dallas from Louisiana to buy drugs from Brown. An argument ensued, however, and

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

Jacquerious Mitchell told authorities he was shot by Brown.

One of the other men then shot Brown, Moore said. Those men fled the scene, and a manhunt was underway for their capture, Moore said. Jacquerious Mitchell was in critical condition in a Dallas hospital, police said.

Moore said 12 pounds of marijuana, other drugs and $4,000 were seized from Brown's apartment.

The NAACP Legal Defense and Educational Fund and some community leaders in recent days had called for an independent investigation into Brown's death and the Dallas police department. Moore said some had suggested police were somehow involved.

"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."

Story continues

Brown's testimony was crucial because he lived on the same floor as Guyger and heard them talking – but said he did not hear Guyger shout verbal commands or warnings before shooting Jean.

Botham Jean's neighbor Joshua Brown, left, answers questions from Assistant District Attorney LaQuita Long, right, while pointing to a map of the South Side Flats where he lived in court on Sept. 24, 2019.

Sherrilyn Ifill, the defense fund's president, said Monday that it is critical to public confidence in the criminal justice system that witnesses who speak out against police violence are fully protected. Ifill said she supports the call by Jean's family for a comprehensive federal investigation of the Dallas Police Department.

“The circumstances surrounding the murder of Mr. Brown cries out for answers,” Ifill said. "We urge state or federal authorities to follow the trail of misconduct left by this case and fully investigate the circumstances surrounding Mr. Brown’s death."

Lawyer S. Lee Merritt, who represents the Jean and Brown families, said Brown had expressed concern to prosecutors about testifying at Guyger's trial. Two months after Jean's death, Brown was wounded by a gunman who killed another man outside a Dallas nightclub. Brown was concerned that the shooter would be looking for him, Merritt said in a social media post Tuesday.

Brown moved to California but went back to Dallas to testify when prosecutors threatened to issue a warrant for his arrest, Merritt said.

"Brown’s testimony was powerful, but it was also duplicative," said Merritt, who has called on the Dallas Police Department to recuse itself from the Brown investigation. "Nothing he testified to couldn’t have been brought in by other witnesses. It wasn’t worth his life."

Consider this: Brandt Jean forgiving, hugging Amber Guyger is one thing — the judge's hug is another

Guyger, 31, told authorities that on the night of the shooting she returned home from an extended shift for the police department when she parked on the wrong floor of her apartment building's garage, walked down the wrong hallway and into the wrong apartment. She said she believed Jean, 26, was an intruder and shot him in self-defense.

Days later, Guyger was charged with murder and was fired. Last week, a jury convicted Guyger of murder and sentenced her to 10 years; under Texas state law, she must serve at least half the sentence to qualify for early release.

Jean's brother, Brandt, and Judge Tammy Kemp hugged Guyger after her sentencing. Kemp also gave Guyger a Bible.

Two days later, police were called to a parking lot where Brown was found lying on the ground with multiple gunshot wounds. He was rushed to a hospital where he was pronounced dead.

"I just spoke with Joshua Brown's mother. She is devastated. We all are," Merritt posted on Twitter the next day. "Joshua Brown was a key witness in the murder of Botham Jean that helped put Amber Guyger away. We need answers."

Contributing: The Associated Press

This article originally appeared on USA TODAY: Joshua Brown murder: 2 suspects in custody after Jean witness killed