BURY, ENGLAND - MAY 24: Rebecca Rigby, the wife of murdered soldier Lee Rigby, grieves during a family press conference at the Regimental HQ of his unit, the Royal Regiment of Fusiliers on May 24, 2013 in Bury, Greater Manchester, England. Drummer Rigby was murdered by suspected Islamists near to his regiment's Woolwich Army Barracks. The UK's security services are facing a Commons inquiry after confirmation that the two men - who were shot and arrested at the scene and remain in police custody - were known to MI5. Credit: Getty Images
LONDON (TheBlaze/AP) -- London is still reeling from the horrific terror attack that took place earlier this week.
Both of the suspects accused of butchering a British soldier during broad daylight on a London street had long been on the radar of Britain's domestic spy agency, though investigators say it would have been nearly impossible to predict that the men were on the verge of a brutal killing.
Still, counter-terrorism officials said they are reviewing what - if any - lessons can be gleaned from the information they had leading up to the slaying Wednesday.
Authorities in the U.S. have similarly pledged to review their procedures in the wake of the Boston Marathon bombing, with the Boston police commissioner saying that cities should consider deploying more undercover officers and installing more surveillance cameras.
The British review comes amid an outpouring of grief over Wednesday's slaughter of 25-year-old Lee Rigby of the 2nd Battalion The Royal Regiment of Fusiliers. Rigby, who had a two-year-old son, had served in Afghanistan. Detectives say they do not believe the attackers knew him or that he was specifically targeted, but they are still investigating.
His anguished widow, Rebecca Rigby, spoke of her loss Friday at a news conference at his unit's headquarters. "I love Lee and always will," she said, sobbing and struggling to speak.
Watch the brief press conference below:
His stepfather, Ian Rigby, read a statement on the family's behalf, including the final text the soldier had sent to his mother, who was too upset to speak.
"The last text he sent to his mum read, 'Goodnight mum, I hope you had a fantastic day today because you are the most fantastic and one in a million mum that anyone could ever wish for. Thank you for supporting me all these years, you're not just my mum, you're my best friend. So goodnight, love you loads," Ian Rigby said.
BURY, ENGLAND - MAY 24: Family members of murdered soldier Lee Rigby, (left to right) Sara McClure , sister, his mother and stepfather Lyn and Ian Rigby, Rebecca Rigby, mother of their two-year-old son Jack, Susan Metcalfe (mother-in-law) and Ray Dutton (brother-in-law) mourn as his stepfather reads out a family statement to the media during a press conference, at the Regimental HQ of his unit, the Royal Regiment of Fusiliers on May 24, 2013 in Bury, Greater Manchester, England. Credit: Getty Images
BURY, ENGLAND - MAY 24: (L-R) The mother and stepfather of murdered soldier Lee Rigby, Lyn and Ian Rigby and his wife Rebecca Rigby, grieve as his stepfather reads a family statement, at the Regimental HQ of his unit, the Royal Regiment of Fusiliers on May 24, 2013 in Bury, Greater Manchester, England. Credit: Getty Images
BURY, ENGLAND - MAY 24: Lyn Rigby (R), the mother of murdered soldier Lee Rigby, is supported by her daughter Sara McClure, whilst she holds a teddy bear bought by Lee for his son, Jack, during a press conference at the Regimental HQ of his unit, the Royal Regiment of Fusiliers on May 24, 2013 in Bury, Greater Manchester, England. Credit: Getty Images
BURY, ENGLAND - MAY 24: Rebecca Rigby, the wife of murdered soldier Lee Rigby, grieves during a family press conference at the Regimental HQ of his unit, the Royal Regiment of Fusiliers on May 24, 2013 in Bury, Greater Manchester, England. Credit: Getty Images
"We are looking at decisions that were made and reviewing whether anything different could have been done," said a British counter-terrorism official who spoke on condition of anonymity because he was not authorized to speak about the investigation. "But you can't put everyone under surveillance who comes on to the radar."
Prime Minister David Cameron said Thursday that the Intelligence and Security Committee would review the work of agencies such as Britain's domestic spy agency, MI5, in the wake of the attack "as is the normal practice in these sorts of cases."
In Britain, security officials operate under the "principle of proportionality," which means there needs to a compelling reason before any type of surveillance is undertaken.
Surveillance can range from watching a person's movements to intercepting phone calls and electronic communication. The greater the level of intrusion into a person's privacy, the higher the level of government approval needed.
Although British police have not named either suspect - both are recovering from their injuries after being shot by police after the killing - they had been known to law enforcement officers for as long as six years, the counter-terrorism official said.
One of the suspects had been photographed at multiple raucous demonstrations by the banned extremist group al-Muhajiroun.
The extremist group, whose name means "The Emigrants" in Arabic, captured attention shortly after Sept. 11, 2001, when it organized an event celebrating the airline hijackers who slaughtered thousands in New York, Washington and Pennsylvania.
But attending such demonstrations, investigators say, is generally not enough to put someone under surveillance or to lead authorities to believe men or women will turn violent. Trolling the Internet for extremist sites is also no proof a person will turn to violence.
Britain is already one of the most heavily watched countries in the world with more than 4.3 million CCTV cameras around the country.
Europol Director Rob Wainwright cautioned against changes that could disturb the balance struck by the "principle of proportionality."
"Investigators have to prioritize their work," Wainwright told The Associated Press. "There are limited resources, but it's not just a question of resources."
Technological advances, for instance, help investigators but also have led to a deluge of data for them to sift through, he said, noting, "The more data you have, the more potential you have for suspects."
Britain, meanwhile, was bracing for potential clashes with right-wing activists, who have promised demonstrations, as well as possible copycat terror attacks in the wake of Wednesday's killing.
Some 1,200 extra police have been put on alert in London.
Wednesday's attack was captured on video by passersby and made for gruesome viewing - one man is seen with his hands stained red with blood and holding two butcher's knives as he angrily complained about the British government and troops in foreign lands.
Analysts say the attackers wanted the publicity to inspire copycats. Already, there has been increased chatter on militant sites, they said.
"We can see the tempo being raised," said Maajid Nawaz, a former jihadist who is now with the London-based anti-extremist Quilliam Foundation. "One of the reasons why these guys acted in this theatrical way was because of the propaganda effect so others would be inspired to do the same thing."
A British government official, who spoke on condition of anonymity because he wasn't authorized to speak about the ongoing investigation, confirmed the increase in chatter since Wednesday's attack but said no specific or credible plots had been detected.
Britain's terror threat level has remained unchanged at "substantial" - the middle of five possible rankings - since the slaying of Rigby.