A schizophrenic who stabbed his baby step-brother to death escaped from a low-security hospital to rape a 14-year-old Chepstow papergirl at knifepoint after being granted 30 minutes "unescorted leave”, an independent inquiry found today.

The report found that an "isolated, inward-looking and incoherent’’ culture contributed to Darren Harkin, 21, scaling the perimeter fence of The Hayes Hospital, near Bristol, and fleeing to attack the teenager.

After he was caught, Harkin was sent to maximum security Broadmoor Hospital indefinitely by a judge at Reading Crown Court after admitting two counts of rape, escape and burglary.

The judge was also told that autistic Harkin was allowed to amass a vast collection of pornographic and horror DVDs while at The Hayes, where he was sent aged 12 for stabbing his six-month-old step-brother to death in his cot.

Today, the National Autistic Society (NAS), which runs The Hayes, said it welcomed the conclusions of the independent report which found the "Hayes culture’’ to be a "causal contributory factor’’ in the tragedy.

Despite being "deeply and expertly committed’’, care staff had not been provided with enough training to ensure a "low-arousal environment’’ for patients, the report said.

The team was unable to offer a "structured account’’ of how Harkin came to have to explicit DVDs in his possession, it added. Nor was his being in possession of the material noted down at any stage during 11-month stay.

Before his escape, Harkin had played pool with his most trusted support worker, the report revealed.

Staff statements taken by the report writers showed Harkin had been allowed to walk "briskly ahead’’ of his supervisors for "some weeks’’.

On the day in question, February 2, Harkin walked through a gate that had been left unlocked "for years’’ and out of his support workers' line of sight, before tackling the fence.

The report stated: "On the material day this was no longer a breach of any procedure as [Harkin] had been granted 30 minutes unescorted leave into that part of the fenced garden area at a recent multidisciplinary team meeting attended by some of [his] clinical team.’’ His conduct was considered "unexceptional’’ and staff expected him to be waiting for them after going out of view for just a few seconds.

The following day the girl was raped on the street while performing her paper round.

The team also found that the Hayes had been in the practice of accepting prisoners and patients from a high-secure units - despite being a "low-security’’ facility.

The report added: "The culture had become isolated, inward-looking and incoherent.

It demonstrated a significant lack of an understanding of the equally valuable role of “forensic awareness" and the need for constant reflective best practice approaches to their resident patients' risk appraisal and assessment.”

The independent external review team interviewed many members of staff, several of whom attacked the lack of risk assessment and training in the facility. One described the procedures as "fluffy’’.

The key contributing factor was deemed to be the lack of a cohesive "oversight and action plan” led by the Executive Board.

The report recommended that dangerous high-security prisoners should no longer be referred to Hayes, and a re-assessment of the risks posed by existing patients.

Mark Lever, NAS chief executive, said: "This was an absolutely terrible incident and my sympathy is firmly with the girl involved and her family.

"I am committed to doing everything in my power to make sure that nothing like this can ever happen again.

"The NAS accepts - in full - the recommendations of the independent inquiry that we asked for. We have already started to take action on several of the points raised. An incident like this must never be allowed to happen again.’’