Laurent Bonomo, 23, was stabbed nearly 200 times, while his friend, Gabriel Ferez, also 23, suffered nearly 50 stab wounds, authorities said while speaking on condition of anonymity in line with police policy. Investigators believe an accelerant was used in the fire, possibly in an attempt to destroy evidence, Britain's Press Association reported.
Neither student had a criminal record.
"I have never seen injuries inflicted to bodies like this before," Detective Chief Inspector Mick Duthie said at a news conference.
Authorities appealed for witnesses in the attack, which took place late Sunday. Authorities found the bodies after responding to reports of an explosion and fire, but only learned how the students died after the post-mortem examination results were delivered Wednesday.
"We are here today because I don't know why these boys were killed or who killed them," Duthie said. "I do believe, however, that those responsible must have been bloodstained when they left."
London has been gripped in recent weeks by a series of stabbing cases involving young people, leading to much soul searching about what has gone wrong with city's troubled youth. But the case of the French students is unique because the pair are foreigners and because of the brutality of the crime.
For a major capital, London has a low murder rate. Police say there were 159 homicides from April 2007 to the same month this year, about a third the number of New York, which is similar in size.
Authorities declined to speculate what might be behind the crime before further toxicology and other tests were completed.
The students were in the second year of a three-year master's degree in bioengineering in France and had been selected to take part in a three-month research project into DNA at London's Imperial College. They were within weeks of returning home.
At the Clermont-Ferrand Polytechnical School in southern France, where Bonomo and Ferez studied, four bouquets of flowers lay in the school's main entry hall.
"It's a huge shock. It is indescribable," said the school's director, Claude-Gilles Dussap. "They were two young people with their lives ahead of them, with goals to fulfill. And they were fulfilling them, because they were brilliant, they were doing internships at Imperial College."
Imperial College Rector Sir Roy Anderson also sent his condolences.
"Laurent and Gabriel had bright futures ahead of them, and it is dreadful that their lives should end so soon," he said.