A paranoid schizophrenic man has been found guilty of manslaughter after he beat a male nurse to death.

The Old Bailey jury heard Jason Cann, then 21, told a psychiatrist he heard Princess Diana's voice urging him to attack Mamade Chattun, 34, in June 2003, at Springfield Hospital, Tooting.

Cann also said he saw the face of the paedophile who abused him as a child superimposed onto the face of Mr Chattun. He claimed he was woken by the nurse known to friends and family as Eshan tugging at his shorts, and he believed the man intended to rape him.

Cann reacted with a frenzied assault which left the father of two unconscious, with severe injuries to his head, body, breastbone, ribs and bowel, and a part of his ear severed, possibly bitten off. Blood was spread on the walls and floor of the lobby of the hospital's John Meyer ward, and on Cann's leg and shoe.

The alarm was raised when another nurse found Cann standing with all his weight on Mr Chattun, jumping up and down "like someone stamping on a cockroach". Mr Chattun died hours later in St George's Hospital.

Cann, who was sedated and required regular breaks during the Old Bailey trial, described the attack, saying: "I got up and started wrestling with him. I got him to the floor and started punching him and kicking him, and stomping on him. I didn't want him to get back up and hurt me."

The judge, Giles Forrester, ruled that Cann should be kept at Broadmoor, the high security psychiatric prison, indefinitely. A murder charge was dropped last week.

The case raised troubling questions about working practices at Springfield Hospital. The killing took place on the day Cann was admitted, but he was left alone unobserved in the ward's lobby area, despite having earlier atta-cked a social worker and refused to take his medication. In 2002, a Mental Health Commission inspection had ruled the lobby should not be used as a patient area.

Mr Chattun went to see the volatile patient alone, despite being warned by colleagues not to go unaccompanied. A post mortem also showed the nurse had cannabis in his bloodstream, and diazepam, despite having no prescription for the Valium-related drug.

The South West London and St George's mental health NHS trust said it would soon publish the report of its own internal inquiry, and confirmed three members of staff were disciplined. A separate inquiry by the Healthcare Commission will now begin.

Trust chief executive Dr Nigel Fisher said: "This was an appalling and unprecedented event. We have done and continue to do everything in our power to prevent anything like this happening again. Although no one could have predicted the ferocity of the assault we know we must provide our staff and patients with the safest possible environment."

He said there had been a major overhaul of 119-year-old John Meyer ward, costing over £750,000, with new CCTV cameras and state-of-the-art alarm system. He commended the Chattun family for their "remarkable dignity" and staff for their professionalism "while grieving the loss of a popular colleague and friend".