The Broward County Sheriff's Office identified 22-year-old Robert Allen as a participant in the execution of the 20-year-old rapper.
XXXTentacion was already popular at the time of his death.
The arrest comes two weeks after Dedrick D. Williams was captured and reserved for the first-degree kill. The BSO news release says only that Boatwright and an armed accomplice confronted XXXTentacion in a robbery attempt, and at least one of them fired a gun. The arrest warrant for Williams explains the two shooters got back into a dark-colored SUV, so they're looking for the driver.
Deputies said Boatwright was one of two gunmen who shot Onfroy.
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According to his arrest warrant, police believe Williams was behind the wheel of the SUV that blocked XXXTentacion from leaving his parking spot at RIVA Motorsports.
Investigators say Mr Boatwright had been detained in jail since his earlier arrest on unrelated drug charges.
Allen is also wanted in Broward County on a felony warrant for violation of probation for drug possession and carrying a concealed firearm.
This July 5, 2018 booking photo, made available by the Broward County Sheriff's, Fla., office, shows Michael Boatwright, who is facing a first-degree murder charge in the killing of emerging rap star XXXTentacion. New reports claim a second suspect connected to the June slaying is now in police custody. "His second album "?" debuted at No. 1 on the Billboard 200 album chart when it was released in March.