Graphic video footage has emerged of a group of California police officers cornering and shooting dead a legally blind and mentally ill man at a gas station convenience store.

The CCTV footage, nearly nine minutes in length, shows a group of five heavily armed officers and a police dog enter the Chevron Station in Fontana after allegedly responding to a 911 call reporting a possible robbery in progress.

They become involved in a stand-off with James Hall, a 47-year-old mentally ill man who was found inside the store.

The November 2015 incident saw Hall – who is registered legally blind and suffering from schizoaffective disorder – appear agitated and try to hide behind the store's shelves as police train their handguns on him.

After about seven minutes into the standoff, he can be seen being chased into a corner by police before appearing to stop and rest on a counter.

Despite not appearing to advance on the officers, Hall suddenly slumps to the tiled floor as he is shot dead.

The grainy surveillance footage was released by lawyers for Hall's family to the Daily Mail on 18 January, about a month after filing a wrongful death lawsuit against the police.

"It's a disturbing video indictment of the officers," said Mark Geragos, whose firm is representing Hall's relatives.

"The video puts the lie to the obviously falsified police account of what happened. In fact, this was an execution."

The video clip appears to contradict the Fontana Police Department's own initial account of the shooting, which claimed Hall "advanced on officers" causing one of its officers to open fire.

The police statement said officers had been called to a possible robbery in progress at 4.15am on 22 November 2015, with Hall allegedly found to be armed with a knife and holding a large rock in his other hand.

"The suspect saw the officers and retreated into the store where the clerk was," the statement said. "Officers went into the store in an attempt to keep the store clerk safe from the armed suspect.

"Officers attempted to talk the suspect into surrendering however he advanced on officers and an officer involved shooting occurred. No officers were injured during the incident. The clerk was located unharmed."

'James was a peaceful person'

police shooting
Fontana police officers seen training their weapons on James Hall minutes before shooting him dead Screen grab of CCTV

The lawsuit filed by the Hall family dispute this account, saying Hall was known to be peaceful and that community members were "fully aware of his disabilities".

It accused officers of escalating the encounter, leading to Hall becoming "startled" and running to the corner of the store where he "cowered".

The lawsuit states: "The Defendant officers cornered Decedent Hall in the rear of the convenience store, brandishing firearms, including an assault rifle. As the Defendant officers continued to surround Decedent Hall, one of them opened fire on him, and Decedent Hall fell to the ground."

It went on to add that a team of around ten officers surrounded Hall's body with weapons drawn, by which point he was already dead.

Hall appears to be carrying something in his hands during the standoff but the grainy footage makes it difficult to distinguish what items they are. At times he appears to be empty-handed.

The lawsuit, filed in San Bernardino County Superior Court, alleges the police were guilty of unlawful use of deadly force and acted "in reckless and callous disregard for [Hall's] constitutional rights".

Hall, who is survived by four siblings, was described by his family as a "peaceful person" who had been awarded a Citizen Citation from the Oakland Sheriff's Office in 2010 for assisting in the rescue of a four-year-old autistic child.

"James was not observed by family, friends, or those who knew him as having violent tendencies because of his mental illness," said Ben Meiselas, an attorney at Geragos & Geragos.

"The family is also puzzled and alarmed by characterisations of the incident as an 'armed robbery' when the only facts released were that James was outside the Chevron station the entire time until police arrived and drew their guns. James lived down the block from the station."