Graphic video footage has emerged of the moment a policeman shot and fatally wounded a handcuffed prisoner being restrained on the floor outside of an El Paso jail.

After shooting Daniel Saenz, 37, in his shoulder, police officer Jose Flores can be seen climbing on top of him and apparently pulling out his taser as another unidentified transport officer continues to restrain him.

Saenz can be seen bleeding and kicking his legs for a few seconds, before lying still on the floor.

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The video has been released on instruction of the Texas Attorney General's Office following a request by The El Paso Times in February. The newspaper requested the video after a grand jury declined to indict Mr Flores over the shooting.

According to a statement by the Combined Law Enforcement Associations of Texas (CLEAT), Saenz had been arrested that day after allegedly attacking an off-duty officer and staff at Del Sol Medical Centre on 8 March 2013. He had been taken there by police when he was found exhibiting “bizarre” behaviour at a supermarket, The Times reports.

Saenz, a body-builder, was then reportedly transferred to the county jail, but needed medical attention after repeatedly banging his head into a doorway.

Warning: This video contains scene viewers may find distressing

The video shows him being dragged along the floor by Officer Flores and the transport guard to an outside area, where a struggle ensues.

CLEAT claims that the guard inadvertently hit the officer's hand during the struggle and after he had pulled his gun from its hoister, causing the gun to fire.

Officer Flores administered CPR almost immediately after gun was fires and Saenz was taken to hospital for treatment but later died of his injuries. An autopsy revealed the bullet from the shot had travelled from his shoulder and into his chest.

In a statement, the CLEAT, representing Flores said: "In the video, Officer Flores first reaches for his Taser. However, he decides not to deploy his Taser because he knew that Mr. Saenz — also earlier that same day — had undergone five cycles of the Taser device, without effect.

“At the same moment Officer Flores draws his weapon, Mr. Saenz pushes off on that curb and, with remarkable strength, sends the civilian escort flying backwards. The civilian escort's arm then hits the trigger hand of Officer Flores, causing his weapon to discharge."

Mr Flores has not been charged with an offence but is believed to be on leave.