A former Philadelphia police officer has been charged with murder for fatally shooting a 12-year-old boy in the back during a chaotic foot chase in early March.

Authorities say that Edsaul Mendoza, 26, engaged in a "tactically unsound" pursuit of Thomas "TJ" Siderio and shot him despite knowing he was unarmed.

Police believed a friend of his was involved in the theft of a weapon.

Mr Mendoza was arrested on Sunday.

According to a presentment of facts released by Philadelphia's District Attorney, Mr Mendoza was part of a group of four plainclothes officers who confronted Thomas and a 17-year-old friend - identified in court documents as "NK" - on 1 March. The officers believed that NK was "tangentially connected" to a stolen firearm investigation.

When they attempted to stop the boys, "a shot went off" and broke a rear passenger window, the presentment added. When the boys attempted to flee, Mr Mendoza chased Thomas and fired at him three times.

The third shot, the document alleges, took place even though Mr Mendoza knew that Thomas' weapon had been discarded some 40ft (12m) away. Thomas had stopped running at the time the final shot was fired.

"Thus, when Mendoza fired the third and fatal shot, he knew the 12-year-old, five-foot tall, 111-pound Thomas Siderio no longer had a gun and no ability to harm him," Philadelphia District Attorney Larry Krasner told reporters on Monday.

"But he fired a shot through his back nonetheless, killing him."

Mr Mendoza was fired by the police force soon after the incident, with the police commissioner saying at the time that the department's use-of-force policies had been violated.

According to Mr Krasner, much of the evidence against Mr Mendoza stems from video footage of the shooting, which will not be released until authorised by a judge. He described the video as "disturbing to watch" and said that Thomas was "essentially facedown on the sidewalk" and possibly surrendering.

Mr Mendoza was taken into custody on Sunday and is being held without bail. A preliminary hearing has been set for 16 May.

A public defender who represented him at a bail hearing on Monday could not be reached. A local chapter of the Fraternal Order of Police has now said it will provide him with a lawyer.

Thomas' great-grandmother, Mary Siderio, was quoted by a local CBS affiliate as saying she was "happy" to hear of the charges against Mr Mendoza.

"I'm so heartbroken, I can't sleep," she said. "None of us can sleep. It's horrible." (BBC)

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