Police say Sampson was among a group of men who fought with Rivera at a dance at the Wayne Bryant Community Center in Lawnside on April 12.
According to investigators, Rivera threw a trash can at Sampson during the fight. Sampson is accused of pulling out a handgun and firing twice in the community center. It is possible one of those shots hit Rivera.
The gunfire spurred a rush from the building, and Sampson and Rivera were among the crowd.
Police say the two fought again outside and Sampson shot and killed Rivera.
Investigators say Sampson was identified by numerous witnesses present at the party.
The April 12 event was billed as a birthday party, but police say the hosts were charging a door fee and among the events being celebrated was another person's release from prison.
Authorities say Sampson was acquainted with the person recently released from incarceration. Sampson apparently worked the door during the party, collecting entrance fees from guests.
Sampson is described as weighing about 150 pounds and standing 5-feet-11-inches tall. Sampson has a number of tattoos, including two black tear drops beneath his right eye, a tattoo of "Jimmer" on the top of his right hand, and a tattoo of "James" on the top of his left hand. The initials M.O.B. are tattooed along the length of his right forearm.
Anyone with information on Sampson's whereabouts is urged to contact Camden County Prosecutor's Office Investigator Eric Wren at (856) 225-8400 or Lawnside Officer Daniel Battista at (856) 573-6204
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