(TriceEdneyWire.com) - The FBI is investigating how a 21-year-old Black man was shot and killed while handcuffed in a Jonesboro, Ark. patrol car on July 29.

“We’ve been asked to get involved,” Kim Brunell, a spokeswoman for the FBI’s Little Rock office, told The Huffington Post Aug. 2. The bureau's ballistics experts will join the probe, she said.

The action came after civil rights leaders called for a comprehensive investigation of the July 29 death of Chavis Carter of Southaven, Miss. even though Jonesboro authorities said that two Jonesboro police officers are on administrative leave and an investigation by local officials is underway into what local police called a suicide.

“The Arkansas State Conference of the NAACP and the Craighead County Branch of the NAACP express our deepest condolences to the family of Chavis Carter, and call upon the Jonesboro Police Department, FBI and Justice Department to conduct a thorough, transparent and unbiased investigation into Mr. Carter’s death,” according to a statement by the two NAACP units released Aug. 3.

Carter was the passenger in a white pickup truck that was stopped by Jonesboro police just before 10 p.m. on the night of July 29, according to the police report. An officer reportedly searched and found marijuana on Carter. A subsequent records check yielded an outstanding warrant for Carter in Mississippi.

“As protocol he was handcuffed behind his back and double locked, and searched,” said Sgt. Lyle Waterworth in an interview with WREG.

But minutes later, officers said they heard a thumping sound and on investigation they found Carter “slumped forward with his head in his lap," and covered in blood. Carter’s hands were still secured behind his back and a small caliber handgun allegedly was found beside him, accordig to the Jonesboro Police Department report. Carter was taken to St. Bernards Regional Medical Center where he was pronounced dead.

Police have concluded that the victim, who they said they searched twice, somehow retrieved a hidden weapon and shot himself in the head.

“Any given officer has missed something on a search, be it drugs, knife, razor blades, this instance it happened to be a gun,” said Waterworth.

“I think they killed him, my son wasn’t suicidal,” said Teresa Carter, the victim’s mother, in an interview with WREG-TV, a CBS affiliate in Memphis.

In addition, she said, he had called his girlfriend from the stopped vehicle, promising to call her from jail. She also said she is puzzled about Additionally, how her son, who was left-handed, could shoot himself in his right temple.