A man pauses at a makeshift memorial for slain soldier Lee Rigby outside… (Dan Kitwood, Getty Images )
LONDON — British authorities on Thursday began combing through their intelligence files and evidence from the attack site to determine whether the apparently terrorism-related killing of a young soldier on a London street could have been prevented.
As political and community leaders vowed not to be cowed by the vicious assault, Scotland Yard announced the arrest of two additional suspects. A man and a woman, both 29, were held on suspicion of conspiring to murder. Investigators gave no further information.
Officers also searched several homes believed connected to the two men who are suspected of hacking the off-duty soldier to death Wednesday in front of stunned bystanders and spouting Islamic political statements before being shot and wounded by police.
MORE: London attack victim was a drummer, machine-gunner, father
British news outlets reported that both men had previously come to the notice of security agencies but were not judged to be planning an attack. The BBC named one of them as Michael Adebolajo, 28, a British citizen of Nigerian descent who the broadcaster said came from a devout Christian family but converted to Islam.
Adebolajo was identified as the man seen in videos brandishing knives in his bloodied hands after the attack and declaring the killing to be payback for the deaths of Muslims in countries where Britain has deployed troops. The suspected accomplice, who police said is 22 years old, has not been named.
The dead soldier was Lee Rigby, a drummer and machine gunner with the Royal Regiment of Fusiliers who had seen active duty in Afghanistan, Britain's Defense Ministry said. Rigby's battalion is based in barracks next to the site of the attack, in the Woolwich district of southeast London.
"We have lost a brave soldier," Prime Minister David Cameron said. "The people who did this were trying to divide us. They should know something like this will only bring us together and make us stronger."
Rigby, 25, is the first person to have died on British soil in an apparent attack by Muslim extremists since the 2005 suicide bombings on London's transit system, in which 52 people were killed. Authorities have since managed to thwart a number of plots of mass killing by Islamic terrorists, many of them "homegrown" radicals, as were the transit bombers.
Investigators are eager to question the alleged assailants in Wednesday's attack to determine whether they acted in league with a terrorist network such as Al Qaeda. Parliament's intelligence committee announced that it would conduct an inquiry on what security agencies knew about the men before the assault.
British news reports said one of the suspects was stopped by authorities last year from traveling to Somalia to join the radical Shabab group.
Police assigned an extra 1,200 officers to patrol London on Thursday. Despite public shock over the hacking death, the British capital — which has been the target of terrorist attacks by Irish republicans and Islamic militants for decades — seemed much as usual.
"Londoners can go about their business in the normal way," Mayor Boris Johnson said after attending an emergency response committee meeting at the prime minister's office Thursday morning.
Security around military installations in London has been beefed up, but defense officials withdrew their initial advice to service personnel not to wear their uniforms in public.
The two primary suspects remained hospitalized in stable condition and were under armed guard. Police searched six residences believed connected to them, one in Lincolnshire in northern England and five in London, including in the district of Greenwich, home to a university where Adebolajo is believed to have studied.
The government's official assessment of the threat posed by international terrorism was unchanged at "substantial," meaning that an attack remains a strong possibility.
Wednesday afternoon's attack took place on a street full of pedestrians. Witnesses reported that the assailants knocked over Rigby with a car, then jumped out and began slashing at him on the ground with butcher knives.
The attackers invited bystanders to film them and seemed to wait for the arrival of police, who shot them when one of them appeared to approach in a threatening manner, according to witness accounts.
A woman who confronted the man identified as Adebolajo emerged as a heroine Thursday for trying to reason with him after the attack.
"I started to talk to him, and I started to notice more weapons and the guy behind him with more weapons as well. By then, people had started to gather around. So I thought, OK, I should keep him talking to me before he noticed everything around him," Ingrid Loyau-Kennett, 48, told the Daily Telegraph.
"He was not high, he was not on drugs, he was not an alcoholic or drunk. He was just distressed, upset," Loyau-Kennett said. "I said, 'Right now it is only you versus many people. You are going to lose. What would you like to do?' And he said, 'I would like to stay and fight.'"
Cameron hailed Loyau-Kennett, a mother of two from southwestern England, saying, "She spoke for us all."
He also warned against tarring all Muslims with the same brush; several mosques in Britain reported being hit by vandals Wednesday evening.
"This was not just an attack on Britain.... It was also a betrayal of Islam and of the Muslim community who give so much to our country," he said. "There is nothing in Islam that justifies this truly dreadful act."