A manhunt was under way on Sunday in Tennessee for a parolee suspected of fatally shooting a Memphis police officer who apparently interrupted a drug transaction when he stopped to investigate an illegally parked car, police said.

The slain policeman, Sean Bolton, 33, was confronted by the gunman and shot multiple times during a brief scuffle after the officer pulled up to the parked car and shined his spotlight on the vehicle, Memphis police said in a statement.

The gunman and another man who was in the driver's seat of the car then fled on foot, and a citizen who found Bolton shot a short time later called for help on the officer's radio, according to police.

Fellow officers arriving on the scene discovered a small bag of marijuana and digital scales in the suspects' car, surmising that Bolton had encountered the two men as they were conducting some kind of a drug deal, police said.

Investigators also recovered a handgun in a field near the shooting scene, the Memphis Commercial Appeal newspaper reported.

Bolton, a U.S. Marine Corps veteran who served a tour of duty in Iraq and joined the Memphis police force in October 2010, was pronounced dead at a hospital.

The driver of the parked car later turned himself in to authorities and has since been released without charge, police said.

But a warrant was issued for the arrest of the suspected gunman, identified as 29-year-old Tremaine Wilbourn, charging him with first-degree murder, according to Memphis police.

The police statement said Wilbourn was on supervised-release from prison, where he had been serving a 10-year sentence for bank robbery, at the time of this weekend's shooting.

The U.S. Marshals Service has posted a $10,000 reward for information leading to his arrest, police said.

Bolton became the third Memphis police officer to be shot and killed during the past four years.