The official, who spoke Thursday on condition of anonymity because he was not authorized to speak about the investigation, said he could not provide other details because the suspects may face trial, the Associated Press reported.
Investigations by Britain’s domestic security service, MI5, can include undercover surveillance, phone tapping and communications intercepts.
Scotland Yard meanwhile confirmed that the victim was a soldier, but did not release his name. The government also lifted its temporary order for members of the military not to wear their uniform in public.
The assailants, who struck the soldier, apparently at random, with their car on Wednesday then attacked him with knives and meat cleavers, are under arrest. Both were hospitalized after being shot by police.
During the night, police raided two homes, one in Greenwich and one in Lincolnshire, in connection with their investigation into the brutal attack.
The Associated Press, quoting an unidentified British official, said both men had been part of an earlier security services probe.
The BBC, quoting unidentified sources, reported that one of the suspects is 28-year-old Michael Adebolajo (pictured) who comes from a devout Christian family but converted to Islam after leaving college in 2001. The BBC said he was described as “bright and witty” when he was at college.
One of the men sought to justify his actions in chilling remarks to a bystander who recorded the attack near the Royal Artillery Barracks in South London on video.
“We swear by Almighty Allah we will never stop fighting you,” he said, clutching knives in his bloodied hands. “The only reasons we have done this is because Muslims are dying every day. This British soldier is an eye for an eye a tooth for tooth. We apologize that women had to see this today but in our lands our women have to see the same. You people will never be safe. Remove your government. They don’t care about you.”
He gave no indication what that land was as he urged people to tell the government to “bring our troops back.” British troops are deployed in Afghanistan and recently supported the French-led intervention in Mali.
Muslim religious groups and charities were quick to condemn the attack and urged police to calm tensions. The Muslim Council of Britain called it a “barbaric act that has no basis in Islam,” adding that “no cause justifies this murder.”
Prime Minister David Cameron, who chaired a meeting Thursday of the government’s emergency response committee Cobra, said the images of the attack were “deeply shocking” but would not deter the British people from standing up to terrorism.
“One of the best ways of defeating terrorism is to go about our normal lives,” he said. “That is what we shall do today.”
The prime minister said confronting extremism is a “job for us all” and praised a 48-year-old Cub Scout leader, Ingrid Loyau-Kennett, who got off a bus to confront one of the suspects and tried to calm him.
In an interview with the the Daily Telegraph, Loyau-Kennett was asked if she was scared, and replied: “No — better me than a child.”
“I thought I had better start talking to him before he starts attacking somebody else. I thought these people usually have a message so I said ‘what do you want?’ said Loyau-Kennett, who lives in Cornwall in southwest England.
It did not seem like he was about to attack her and “the policeman was the next target,” she said.
Loyau-Kennett said she was not scared and that the armed men did not seem to be drunk or on drugs. She said she was trying to keep them occupied so they didn’t get more agitated.
She reboarded her bus shortly before police arrived, watching as police shot the two suspects, the BBC reported.