Burglary link to 'brutal' double murder

(CNN) -- British police investigating the horrific murder of two French students in London Thursday are exploring the possibility it was linked to an earlier burglary.

Police revealed that a laptop had been stolen from the flat in New Cross, south London six days earlier.

The British Press Association reported Friday that forensic experts found no evidence of forced entry and one line of inquiry is that a stolen set of keys may have been used.

Laurent Bonomo and Gabriel Ferez, both 23, were found inside where they had been bound, gagged and stabbed to death in what police described as a frenzied attack.

The officer leading the inquiry, Detective Chief Inspector Mick Duthie, told a press conference Thursday he had "never seen injuries inflicted to bodies like this before". He said: "The extent of the injuries are horrific. Everyone working on this case, including myself, has been deeply shocked by what we have seen." Watch CNN report on murders »

Police said both men were "entirely innocent", with no criminal background in either France or the UK.

The British Press Association also reported that Bonomo's fiancee, Mary Bertez, was the last person to speak to him in the early hours of Sunday morning. Writing on a social networking site, she said: "My love, we were always together but unfortunately I wasn't there that evening.

"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."

Bonomo and Ferez were students at Universite Blaise-Pascale in Clermont Ferrand, France. They had arrived in London in late May to do research at Imperial College and were planning to return to France at the end of July.

Firefighters found the students' bodies Sunday night after responding to a fire at Bonomo's rented room on a quiet cul-de-sac in south London, police said. They initially believed the men died in the fire, but a post-mortem exam showed they died of the stab wounds.

The fire was the result of an explosion, Duthie said, and the smell of accelerant permeated the area.