French students were bound, gagged and stabbed 250 times

Two French students were tied up, gagged and stabbed nearly 250 times before being set on fire in a flat in south London, police revealed yesterday.

Laurent Bonomo and Gabriel Ferez, both 23, moved to Britain two months ago to undertake a three-month placement at Imperial College London. They were tortured and brutally murdered by an intruder who broke into M. Bonomo's flat in New Cross on Sunday night as they were playing a computer game.

M. Bonomo's fiancée, Mary Bertez, had visited him frequently while he was in London. She wrote a poignant message last night on his page of the social networking site Facebook. "My love, we were always together," it read. "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."

Another friend, Laurent Maxence, wrote: "From where you are with Gabriel, we are thinking of you and I hope that the stars are watching over you."

Senior police officers said yesterday they were baffled by the attack. One theory is that the pair were attacked by a burglar who had broken into the flat six days earlier and returned on Sunday to kill them. Another, more unlikely, suggestion is that they were victims of mistaken identity.

At a press conference at Scotland Yard, Detective Chief Inspector Mick Duthie described the injuries inflicted on the pair as the worst he had encountered in his policing career. "I have never seen injuries inflicted to bodies like this before," he said, before adding: "We are here today because I don't know why these boys were killed or who killed them."

Neighbours described how the they heard a loud explosion coming from the small redbrick ground-floor flat. Farzana Akbary, a 27-year-old from Afghanistan, said: "I was washing the dishes at my kitchen window. All of a sudden there was a fire, a blast. It blasted out both windows. There was smashing glass and everybody was watching from their windows. Then the ambulance came. I didn't hear any screaming or anything and I didn't know the people that lived there."

Another neighbour, who asked not to be named, said: "I heard three bangs; one really loud one followed by two smaller ones. It was like somebody dropping something really heavy. It shook the whole building. I ran downstairs and saw flames and black smoke and called the fire brigade.

"There were other residents out throwing water through the windows to try and put the flames out. Then they were leaning in and shouting, trying to find out if there was anybody there. When we got no response we assumed that the house was empty and that it had just been a fire. It wasn't until later we heard that two bodies had been pulled out."

It was thought initially that that the two men died in the fire, but a post-mortem examination revealed the extent of their injuries and a murder inquiry was launched. The police's progress has been hindered by a number of factors, not least the fact that the pair appeared to have had very few acquaintances in London, having only moved to Britain recently. They did not know each other before they arrived from France.

While only a single bouquet of flowers was laid outside 12 Sterling Gardens, the scene of the murders, in France their deaths were being grieved by a wide circle of friends and family.

Tributes to the pair came from Imperial College, in South Kensington, and from the Polytech' Clermont-Ferrand, their college in the Auvergne.

The pair had been in the country since May after gaining sought-after places at Imperial College, where they were planning to study bio-engineering in the college's laboratories for three months.

While mystery surrounds the killings, what is known is that on 29 June, Gabriel Ferez travelled from his flat in South Norwood to his friend's flat in New Cross to play a computer game.

At some point on that Sunday evening the pair were confronted by an intruder who bound and gagged them in the living room of the bedsit. In the frenzied attack that followed M. Bonomo was stabbed 196 times in the head, neck and body while M. Ferez was stabbed 47 times.

The intruder then doused their bodies and the flat with some sort of accelerant, possibly petrol, and set the victims and the flat on fire. The hunt for the killer is focusing on a white man who was seen running away from the scene. Police say that he was seen running away on foot, but some reports say a neighbour saw a man "speeding off in a BMW" shortly after the resulting explosion.

At a press conference yesterday morning, the police were asked about a possible motive for the killings. While admitting that they had no idea why anyone would want to kill the pair, neither of whom had a criminal record in Britain or in France, detectives did reveal they were pursuing several lines of inquiry.

One of these is that M. Bonomo and M. Ferez were killed by someone who was looking for someone else. Asked if it this could have been the case, Det Ch Insp Duthie said: "That is one line of inquiry. 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. They were here as students."

Another theory is that they were killed by someone who was burgling the ground-floor flat and killed the men when they disturbed him.

M. Bonomo's flat was broken into six days before the killings. During that break-in a laptop computer was stolen although the intruder was scared off when M. Bonomo emerged from the shower.

It has been suggested that the killer was this previous burglar who had also managed to steal some keys and had returned. There was no sign of forced entry at the building. Police added that the killing would have taken some time and left the killer drenched in blood. "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," Det Ch Insp Duthie added.

Nicky Crowhurst, 25, a student who shared a laboratory with M. Ferez, said: "It's a huge shock. I can't believe it. Him and his mate were always in the lab. They had only been here a little while. He was a quiet guy but really friendly."

Professor Stephen Matthews, who worked closely with M. Bonomo, said the Frenchman was an intelligent young student with a bright future. He said the keen chess player had fitted in quickly and made friends in the department.

"They were both very likeable chaps," he said. "Laurent was particularly mature and well-rounded. He was a keen tennis fan and looking forward to following the French players at Wimbledon.

"Laurent was very well-liked. He was intelligent and he obviously had a bright future. We are all stunned and shocked, to say the least. Our thoughts are with their families and Laurent's girlfriend."

In France, Claude-Gilles Dussap, the director of the Polytech' Clermont-Ferrand, said the campus was in shock at the loss of two of its most promising students. He said: "They were very good and very pleasant students. We had absolutely no problems with them, and we were sure they would find a professional position without any problems anywhere in the world.

"They were mature, sensible, very well-tempered. They had no problems about being understood by other students. The teachers and the other students are very very shocked."

Fiancée's grieving message on Facebook

Mary Bertez posted a message on the Facebook page of her fiancé, Laurent Bonomo, as details of the double murder were revealed by police.

She wrote: "My love, unfortunately I was not there that night – we, who were always together. I think about you every single second. I have had 10 months of happiness that I never experienced before. Today, you are gone andI will try to be the example you always wished for. I will give the investigation all the information necessary, my darling, so that you can be avenged. I love you from the bottom of my heart."

Before his death, she had left messages saying how much she missed him. "Come back quickly, mon chou!!! London is too far away. Sniff! Love you to death. Your princess."