By Ben Ando and Daniel Sandford
Gabriel Ferez and Laurent Bonomo were stabbed 244 times at their flat
The conviction of Dano Sonnex and Nigel Farmer for the murders of two French students in New Cross, south east London, raises uncomfortable questions for the probation service, the courts and the police.
Justice Secretary Jack Straw has already apologised to the families of the two victims, and the head of the London probation service has resigned.
Why? Because, as the BBC can now reveal, Sonnex should never have been free to kill on 29 June last year.
Six weeks earlier magistrates had granted him bail on charges of handling stolen goods.
He was expected to be recalled to prison to serve the remainder of an earlier sentence but the paperwork was not ready and he walked free from court.
In May 2002, when Sonnex was 16, he stabbed another youth, Ersan Topcu, in a row over a car, and in September of that year, took part in a spate of robberies with a friend.
In one, they robbed a woman and three men of their bags and wallets and in another they tried to steal from a Chinese takeaway. In both, Sonnex fired a gun - though it was only loaded with blanks.
In the second robbery he was chased by the owner of the takeaway, Ngliep Lugia, and was apprehended, despite producing a knife.
Mr Lugia told the BBC he had been trained in kung-fu as a child and was determined to stop Sonnex.
In March 2003, aged 17, Sonnex admitted various robbery and violence charges and was sentenced to eight years in jail.
In prison he quickly emerged as a troublemaker and was involved in 41 separate incidents, including setting fire to his cell.
Sonnex had been drinking and took drugs the evening before the murders
He applied for parole in July 2006 and June 2007, but both applications were refused.
But by February 2008 he had reached the two-thirds point in his sentence and his release was mandatory.
Despite his history he was assessed as only medium risk to the public and it was agreed he would reside at his family home.
He walked free on 8 February 2008. Up until that point Dano Sonnex had been in police custody his entire adult life.
Three days later, the police were called to a flat after allegations he had tied up a man and woman and made threats.
Although the police investigated, the witnesses did not make any statements and no charges were brought. His probation officer gave him a verbal warning.
During this period, probation records show he complied with his appointments and usually arrived early. His behaviour was described as "polite".
But on 28 April 2008 he missed an appointment with his "offender manager" - the new name for probation officers - because he had been arrested in connection with handling stolen goods.
He was charged, remanded in custody by magistrates, and sent to Belmarsh prison in south-east London.
At that point the probation service started the process of rescinding Sonnex's licence and recalling him to prison to complete his original 2003 sentence.
But something went wrong.
On 16 May he was still in prison when he appeared again before magistrates. The BBC understands that the magistrate believed Sonnex's licence had been revoked, and he would be returning to prison.
On this basis, Sonnex was given "technical bail" and released since remanding him in custody would serve no purpose.
But the paperwork revoking his licence had not been completed.
The process was then subject to several weeks of delays, partly because probation officers did not know Sonnex had got bail.
In addition, probation bosses - possibly feeling under pressure from the Ministry of Justice to keep prison numbers down - wanted to make sure they had all the right information.
Harry Fletcher, of the National Association of Probation Officers (Napo), said: "During that time again on file there are numerous attempts by the probation officer to obtain the information from the police, from the courts, CPS and - remember she's also working on a hundred other cases probably as complex - and the information is not forthcoming."
Sonnex's licence was not formally revoked until 13 June. But this was a Friday afternoon, and local police did not learn of the recall notice until the following Monday.
It would be nearly two weeks before police finally went to the Sonnex family home to find him.
They knocked on the door on 29 June. It was a complete coincidence but the two French students had been killed only hours before.
The failures in dealing with Sonnex were so bad Mr Straw feared the case would become the criminal justice system's "Baby P".
Mr Straw forced the Head of the London Probation Service, David Scott, to resign.
The justice secretary said: "There were a series of really serious failures by the court and the CPS at the original bail hearing when he was inexplicably given bail, and then subsequent to that failure by the London Probation Service and by the police."
Senior probation officers admit there were failures in this case, but warned the system for protecting the public will never be perfect.
Steve Collett, of the Probation Chiefs Association, said risk can be minimised and managed but not eliminated.
"There will always be people who go on and commit further offences of the most serious nature whatever we do and however we manage them," he said.