Officers had responded to an emergency call in Wilmington from a man who had apparently shot himself.

When they arrived, they found Jeremy McDole in his wheelchair "still armed with a handgun", according to Police Chief Bobby Cummings.

The footage shows an officer approaching the 28-year-old with a gun drawn, shouting "show me your hands" and "drop the gun".

Other officers then appear in the video also with their guns drawn, shouting similar commands.

Mr McDole can be seen moving around in his wheelchair, before he reaches into his jeans and the officers fire multiple shots. He then slumps out of his wheelchair to the ground.

His mother, Phyllis McDole, told a news conference on Thursday that her son's death was "unjust". She said: "He was in a wheelchair, paralysed from the waist down.

"There's video showing that he didn't pull a weapon... I need answers."

Chief Cummings said officers "engaged" Mr McDole as he was removing the gun from his waist. He added: "I assure that not one of those officers intended to take anyone's life that day."

The shooting is being investigated by the department's criminal investigation and professional standards units, along with the Delaware Department of Justice's Office of Civil Rights and Public Trust.

Eugene Smith, Mr McDole's uncle, said he was with his nephew 15 minutes before the shooting.

He said: "He had a book bag, but I never seen a gun. It was an execution. That's what it was. I don't care if he was black, white, whatever."

All four of the officers are currently on administrative duty. One has been on the force for 15 years, while the others have been there for around five years, Chief Cummings said.

Mr Smith said his nephew had been released from prison last year and was living in a nursing home.

Mr McDole has convictions for drug possession and disorderly conduct. He was paralysed when he was shot in the back in 2005 by a friend with whom he had been smoking marijuana, according to court documents.