The FBI says it is "monitoring" the case of a police suspect who officers claim fatally shot himself in the head despite having his hands cuffed behind his back in the rear of a patrol car.

Chavis Carter died last Saturday after being picked up in a traffic stop in Jonesboro, Arkansas, during which drugs were discovered in his vehicle.

The 21-year-old black man had been searched twice by officers, but a handgun that officers say the suspect later used was not found. Questions have also been raised as to how the left-handed Carter was able to deliver a fatal shot to his right temple while in restraints, as it has been claimed.

On Friday, the FBI confirmed to the Guardian that local police had shared "investigative information" relating to the incident and that federal agents would "monitor and assess the situation".

Chavis died from a single gunshot wound to the head on Saturday night. He had earlier been detained – alongside two other suspects – by officers searching for drugs in the back of a truck they had noticed parked in the street with its lights on.