Two French research students found stabbed to death following a flat fire had been tied up and suffered horrific, excessive injuries, police have said.
The bodies of Laurent Bonomo and Gabriel Ferez, both 23, were found in a ground-floor flat in New Cross, south-east London, on Sunday night.
They had suffered a total of 243 stab wounds to the head, neck and chest before being set alight.
The biochemistry students had been studying at Imperial College, London.
Det Ch Insp Mick Duthie said he had no idea why the students were killed.
Speaking at a news conference at Scotland Yard, he said the flat had been broken into six days before and a laptop had been stolen.
He also said a white male was seen running from the scene of the fire, but police have not ruled out the possibility others might have been involved in the murders.
Police said they were shocked by the crime
Mr Bonomo's fiancee, Mary Bertez, wrote a tribute to him on the social networking website facebook.
She said: "I will never stop thinking about you for a second. I had 10 months of a happiness I had never experienced until then.
"Today you are gone. I will try to be as good as you always wanted.
"I will give all the required information to the investigation, my dear, so you can be avenged."
Mr Duthie said one line of inquiry was that the attack was a case of mistaken identity.
"We cannot find anything in these two young men's background to suggest they were involved in any criminality, that they had done anything wrong," he said.
'Frenzied, horrific attack'
The BBC's crime correspondent Ben Ando said Mr Bonomo had 196 stab wounds, including 100 to his back, and Mr Ferez had been stabbed 47 times.
He added a chemical was used as an accelerant in the fire.
Mr Duthie said: "The extent of the injuries are horrific. I have never seen injuries like this throughout my career.
"I would not say this was a professional attack. I would say it was a frenzied, horrible, horrific attack.
"I imagine it would take some considerable amount of time to inflict the nature of the injuries."
Mr Bonomo's fiancee Ms Bertez said she will never stop thinking of him
The detective said no weapon had been recovered during extensive searches in the area and police were studying some "limited" CCTV footage.
Mr Duthie said the postgraduate students had been in London since the beginning of May and were due to return to France at the end of July.
Imperial College's Rector, Sir Roy Anderson, said the students had "bright futures ahead of them".
The emergency services were called after residents reported an explosion in Sterling Gardens on Sunday night.
Mr Ferez, who lived at another south London address, was visiting his friend when the attack took place.
Mr Duthie said Mr Bonomo was known to be alive in the early hours of Sunday morning because he spoke to his girlfriend in France.
The parents of the two men are in the UK and have had to identify their sons, police said.
Police said Mr Bonomo, of Velaux, and Mr Ferez, of Prouzel, studied in Clermont-Ferrand, central France, and had been chosen to take part in a research project into chains of protein within DNA at Imperial College, which was due to last up to four months.
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