DALLAS (AP) - Police in Dallas continue to search for a third suspect in the killing of a witness who testified at the murder trial of a former Dallas police officer.

Investigators say 22-year-old Thaddeous Green remains at large Wednesday following the shooting death last week of Joshua Brown in what police say was a drug sale that went awry.

Dallas police said in a statement late Tuesday that 32-year-old Michael Mitchell was taken into custody in Marksville, Louisiana. The third suspect, Mitchell's nephew, 20-year-old Jacquerious Mitchell, was in critical condition in a Dallas hospital following an exchange of gunfire with Brown.

It is unclear why the men drove more than 300 miles (483 kilometers) from central Louisiana to purchase marijuana in Texas.

Brown testified in the trial of Amber Guyger, who was sentenced last week after being convicted of murder in the shooting of Botham Jean.

Prosecutors say Guyger mistook Jean's apartment for her own and believed he was an intruder.

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