EXCLUSIVE

XXXTentacion's murder case has expanded beyond the scope of the Broward County Sheriff's Dept. in Florida ... TMZ has learned federal investigators are also involved in tracking down his killers.

Sources familiar with the situation tell TMZ ... the U.S. Marshals and Broward County Sheriff's Dept. are on an intense hunt to track down at least 2 other suspects who disappeared after Dedrick D. Williams was arrested last week for murder.

We're told the Marshall has been at the forefront from the beginning ... the Office played a major role with the Broward County Sheriff's Dept. in nabbing Dedrick. But as we first reported ... cops believe 3 people were involved in the murder of the 20-year-old rapper, and arrest warrants have been issued for the remaining 2.