Three down, one to go -- another one of XXXTentacion's alleged murderers is in custody ... thanks to the U.S. Marshals.
Robert Allen was arrested Wednesday in rural Georgia. According to jail records, he's currently being held in Dodge County. The Marshals Fugitive Task Force reportedly found him at his sister's home in Eastman, GA.
Cops say his sister was cooperative when officers showed up to make the bust.
Allen was the guy who was originally wanted as a person of interest because he was caught on surveillance video outside the motorcycle dealership where XXXTentacion was moments before his murder. As we reported, a grand jury indicted him last week for first degree murder and armed robbery with a firearm.
He'll be extradited to Broward County, FL to face the charges, along with 2 others -- Michael Boatwright and Dedrick Williams.
Trayvon Newsome, who cops have named as a trigger man in the rapper's murder, is the only suspect still at large.