"I wasn't surprised that it happened," Barra said of Wednesday's attack. "... Britain is only responsible, the government. And I believe all of us, as a public, we are responsible. We should condemn ourselves, why we did not do enough to stop these wars going on in Iraq and Afghanistan."
The Woolwich bloodshed spurred concerns not only about violence by Islamic extremists but also about attacks targeting Muslims by people angry about Rigby's killing.
"People can only take so much. And people will break," said Victor Easdown, a construction worker who heard shots ring out in Woolwich as police took on Rigby's attackers.
In Kent, police arrested a man on suspicion of "racially aggravated criminal damage" at a religious building. And Wednesday night in Essex, a man with two knives was arrested after throwing a smoke grenade at the Al Falah Braintree Islamic Center and demanding someone come outside to answer to the Woolwich slaying, the mosque's secretary Sikander Sleemy said.
Members of the far-right English Defence League clashed with police late Wednesday, with a tweet from its official account touting that "it's fair to say that finally the country is waking up!:-) NO SURRENDER!"
"Don't listen to the Government cover ups, The lies about Islam being peaceful," read another EDL tweet Thursday.
Political and social commentator Mohammed Ansar appealed for "a sense of calm (and) perspective" after what he called "a really, really heinous act of, I would say, criminality, ... not terrorism."
"What we don't need are knee-jerk reactions ... to really ratchet up tensions and really stoke and inflame anxieties within communities," he told CNN.
Paper: Woman says she talked to attacker
The attack may have wide-ranging repercussions in Britain, including possibly enflaming sectarian tensions and leading to more violence.
But it's already have an impact on people who live and work in Woolwich -- the working-class, multicultural neighborhood where the mutilation took place -- and witnessed the carnage firsthand.
A man who identified himself as James told London's LBC 97.3 radio station that he saw two men standing by the victim, who was on the ground.
At first, James thought they were trying to help the man. But then he saw two meat cleavers, like a butcher would have.
"They were hacking at this poor guy, literally," he told the radio station. "These two guys were crazed. They were just not there. They were just animals."
Amid the horror, an individual story of courage emerged Thursday in the person of a Cub Scout leader named Ingrid Loyau-Kennett.
Loyau-Kennett told Britain's Daily Telegraph newspaper that she had jumped off a bus to try to revive a man -- later determined to be Rigby -- she thought had been hurt accidentally.
She swiftly realized the man was dead, and it was no accident.
"When I went up, there was this black guy with a revolver and a kitchen knife. He had what looked like butcher's tools, and he had a little ax, to cut the bones, and two large knives, and he said, 'Move off the body,' " she told the newspaper.
"So I thought, 'OK, I don't know what is going on here,' and he was covered with blood. I thought I had better start talking to him before he starts attacking somebody else."
Unarmed police -- like most in Britain -- arrived at 2:29 p.m. Wednesday, nine minutes after the first call came in police. Armed officers were on site five minutes later. Witnesses recounted the suspects then ran at the police, who responded with gunshots.