By Ben Ando
Crime correspondent, BBC News
Both Sonnex and Farmer denied murdering the two students
At 22:11 BST on Sunday 29 June 2008, the fire brigade received a call from a member of the public reporting a fire in a flat at Sterling Gardens, New Cross.
When they arrived, firefighters found the flat ablaze and the front windows blown out. Once inside, they came across a scene of "unimaginable horror", which would cause revulsion and heartbreak on both sides of the English Channel.
There were two bodies - those of French students Gabriel Ferez and Laurent Bonomo - and both had been subjected to horrific violence.
Post-mortem examinations revealed they had been bound and stabbed repeatedly - between them almost 250 times. The fire was then started deliberately.
From the outset, there seemed to be two questions that needed answering: who would have cause to attack two well-liked students and why were such horrific levels of violence necessary?
Detectives hunting the killers immediately considered the options - were the students deliberately targeted by enemies in their own backgrounds, or were they simply the victims of random violence?
Friends described them as quiet and studious and popular. They had only been in London for a few weeks and it was clear they had nothing in their lifestyles to suggest a motive for the killings.
Investigations quickly revealed that their mobile phones and computer games were missing from the flat, and there had been withdrawals at cash machines in the area using their cards the morning after they were last seen alive.
It was beginning to look as though this was a burglary that had gone horribly wrong.
Nigel Farmer gave himself up at Lewisham police station
A neighbour had seen a man leaving the flat just before the fire and provided enough information to create an artist's impression of the suspect.
It was this that would give police their big breakthrough.
In the early hours of Monday 7 July, a man walked into Lewisham police station in south London.
He told the desk clerk he wanted to speak to a detective and while he waited he told a young woman in the waiting area he was one of those wanted for two murders.
He also applied cream to his hands and face, which appeared to be burned and blistered.
When arrested, the man gave his name as Nigel Farmer. He was taken to hospital and treated before being questioned. He said nothing, and was charged with the two murders.
'Bite his face off'
In the meantime, police had been studying CCTV images recovered from the New Cross area and eventually a key figure emerged - a figure that detectives believed could be Dano Sonnex.
Sonnex, 23, was a known violent offender who had spent just four months of his entire adult life outside prison. When arrested, he told one officer that he would "bite his face off."
By now, the painstaking forensic work was also yielding significant clues. Bloody fingerprints were found in the flat next to a palm print - the fingerprints were unclear, but the palm-print was a match for Sonnex.
The police also arrested a young woman called Fay Culyer, who was in a relationship with Sonnex's brother.
Students Gabriel Ferez and Laurent Bonomo were studious and well-liked
She told them that Nigel Farmer had called her boyfriend's mobile phone early on the morning of the murders, and that she had overheard him threaten to "cut off the hand" of someone he was with.
In court, 33-year-old Farmer told the jury he had been with Sonnex on the morning of the murders, but had then returned to the Sonnex family home where he had been staying.
Sonnex, he said, had come in later - covered in blood. Farmer did admit then going to the flat and starting the fire, but said he did so in the face of threats from Sonnex and his family.
Sonnex had another version of events. He claimed he had been at the flat with Farmer and that they had tied up the students and taken their cash cards.He said that when he returned to the property from a cash machine, Farmer had already killed them.
But the police had a different idea. Their case was that Farmer and Sonnex, together, were looking for places to burgle and had returned to the students' flat because a few days before they had managed to steal a laptop.
Then they both murdered them before making off with just a few belongings and less than £400 in cash.
The final, bitter irony is that the students' horrible deaths may have been the result of a tragic blunder.
When he went to the cash machine, Sonnex was able to use Laurent Bonomo's cash card successfully.
Then he tried to use Gabriel Ferez's card, but it was retained. Detectives suspect that Sonnex believed Ferez was trying to trick him by giving him the wrong PIN code. He flew into a rage and returned to the flat with murder in mind.
But transaction records show that Sonnex had the correct PIN - he'd been able to read the card's balance first - but then when he re-entered it to withdraw cash he apparently got the digits wrong.
It was a mistake that Laurent Bonomo and Gabriel Ferez paid for with their lives.