By Dominic Casciani Community affairs reporter, BBC News website

Robert Stewart had a Ku Klux Klan sign in the cell

The family of Zahid Mubarek have waited six years to find out why the teenager was murdered in a young offenders' institution.

But while the public inquiry heard months of exhaustive evidence, the presence of one very disturbed young man hangs over the testimony.

And it is deeply complex questions about the mental state of Robert Stewart that pose some of the most awkward questions for the Prison Service as the inquiry is published.

Stewart, originally from Greater Manchester, arrived in Cell 38, Swallow Unit, on the morning of 8 February 2000.

Jailed for 175 days for vehicle offences, he had been transferred to await trial for sending letters harassing a London woman.

Born in 1980, he had had a troubled childhood and was excluded from secondary school after an arson incident. A separate arson attack led to his first conviction at 13.

A consultant psychiatrist said the teenager displayed signs of a personality disorder - this would be the last psychiatric examination until after the murder.

By the time he arrived at Feltham, in west London, Stewart had 18 convictions for 70 offences. But it was during the early stages of his imprisonment in 1997 that his behaviour rang alarm bells.

MEDICAL REPORT He told me, as I remember, that Stewart was a psychopath - he explained that to me as meaning Stewart had no conscience or remorse about what he did Prison officer James Farrell

On one occasion he flooded his cell, smeared excrement on the walls, covered himself in margarine and placed a noose around his own neck.

Later, after being mistakenly told he was to be released, he was found to be talking to cell walls.

The following month he was seen eating soap and swallowing a screw. He later set fire to trousers he was wearing. A nurse recorded Stewart and another prisoner inciting each other to harm themselves.

One file note warned the inmate could be a very dangerous young man. It was during his imprisonment at yet another jail, Stoke Heath, that that warning was confirmed.

On 23 June 1998, Maurice Travis, a prison pal of Stewart's, stabbed to death another inmate, Alan Averall.

Although Travis wielded the weapon, the authorities remain convinced that Stewart played a part, perhaps more than by just egging on his friend.

In the two years before Stewart murdered Zahid Mubarek, there had been only five prisoner-on-prisoner killings. Stewart had been implicated, but not charged in one of those deaths.

'Stewart a psychopath'

In November 1999, Stewart was back inside at MHP Altcourse. While some staff thought his behaviour was improving, one senior officer, James Farrell, harboured doubts and asked a mental nurse, Chris Kinealy, to talk to the inmate.

MISSED OPPORTUNITIES TO STOP STEWART? Stewart involved in an earlier murder No psychiatric treatment provided Prison intercepted racist letter Searches missed makeshift dagger Feltham officers ignorant of Stewart's past Racist killer's intent missed

"Kinealy agreed to speak to Stewart," said Mr Farrell in his original police statement. "I was not present but afterwards he told me, as I remember, that Stewart was a psychopath. He explained that to me as meaning Stewart had no conscience or remorse about what he did."

Mr Kinealy had concluded Stewart had an untreatable personality disorder condition. This would place Stewart in a very small group of extremely difficult and potentially dangerous cases where, at present, the law and medicine have few answers.

However, even if his condition were medically untreatable, no other practical action appeared to have been taken.

And, it was with this question mark hanging over his mental state that Stewart ended up sharing a cell with Mr Mubarek.

When Stewart arrived at Swallow Unit on 8 February 2000, the duty man on the wing placed him in the only spare bed - in Mr Mubarek's cell.

The officer apparently had "almost literally nothing" with which to form an opinion about Stewart. While he had been moved into the prison, it appeared that his security files lagged behind him - or at the very least - they were not sufficiently distributed among the officers.

During the period when he arrived, Feltham was buckling under the strain of massive daily shifts in population. Over one month alone, Feltham received 415 new inmates.

With extremely high levels of staff sick leave and low morale, the inquiry heard evidence that officers on duty were essentially crisis-managing the prison.

Was Stewart a disaster waiting to happen thanks to, as lawyers for the Mubarek family put it, "terminal incompetence" of the Prison Service?

One senior officer, Steven Martindale, told the inquiry that he had been called in to look at the inmate's file because his colleagues were concerned at what it said.