An inquiry is being carried out into why a schizophrenic who stabbed a man to death had been wrongly released from custody just hours before the attack.
Anthony Joseph had been released from custody in Manchester but should have been detained to face burglary charges.
Within hours of his release he stabbed 28-year-old Richard Whelan seven times after throwing chips at his girlfriend on a London bus.
Joseph admitted manslaughter on grounds of diminished responsibility.
He will be sentenced on 20 December.
The Old Bailey heard how Joseph turned on his victim after throwing chips at passengers on a bus on the Holloway Road in July 2005.
Mr Whelan, a hospitality worker, was stabbed through the heart but a jury trying Joseph for murder twice failed to reach a verdict and the prosecution then accepted his manslaughter plea.
After the conviction, the government said: "This case shows a number of failings for the criminal justice system as a whole which is of great concern to the government and which we are investigating."
The inquiry could reflect on the fact that the government did not know how many prisoners had outstanding arrest warrants against them, said BBC home editor Mark Easton.
The names on the prisons computer did not link up with the names on the police computer, he said.
Joseph was released from custody in Manchester only a few hours before the attack on 29 July 2005.
Mr Whelan was stabbed to death on the top deck of the bus
He had been arrested by Surrey police and remanded in custody on 10 June, on charges later dropped that related to an alleged abduction and unlawful sex with a 15-year-old.
After the charges were dropped, he should have been detained because there was an arrest warrant out for him in connection with an alleged burglary.
The warrant had been issued when he failed to appear for a hearing at Liverpool Crown Court on 27 June.
Arrangements had been made for him to be taken from a privately-run young offenders institution in Manchester to Liverpool Crown Court to face the burglary charges.
Although the details were on the Police National Computer, the prison was not aware of the situation.
Merseyside police did not know Joseph had been in custody; it is understood the computer had not been updated with that information.
The defence said Joseph was suffering from the onset of paranoid schizophrenia when he carried out the attack on Mr Whelan, of Kentish Town, north London.
But Mr Whelan's family said in a statement that they believed "the defence of diminished responsibility in this case has been used as a defence for the undefendable".
The evidence, they said, showed that Joseph was "an angry and vindictive man".
It added: "He has tried to excuse his actions that evening by claiming mental illness, however in our opinion he callously killed Richard for no reason at all."
In a statement from Surrey Police Authority, its chief executive Sue Martin said they were "very sad about the tragic death of Mr Whelan".
She said they were waiting for the outcome of a review into why Joseph was not in custody at the time he killed Mr Whelan.
'Efficient and effective'
The Labour MP, Keith Vaz, who chairs the Home Affairs Select Committee, told BBC News the information about Joseph should have been readily available.
He said: "We shouldn't be going over old ground again because this is something that ought to have been sorted out after Soham.
"There ought to be a national computer that is efficient and effective. The information ought to have gone on immediately."
Shadow home secretary David Davis called on the government to "get a grip".
"It should have a database of prisoners against which it can compare those people who should be in prison and should not be out on the streets, able to carry out vicious crimes like this," Mr Davis said.
Det Ch Insp John Macdonald said he was "disappointed" that Joseph was not convicted of murder.
"Our view all the time was that he was guilty of murder, he had the mental state to commit murder not manslaughter," he said.