Both of Lee Rigby's killers were driven by a warped extremist ideology that in their eyes justified picking a man they assumed was a British soldier at random and hacking him to death in the street.
Michael Adebowale and Michael Adebolajo each owned speeches and books about religious war and martyrdom, including works by U.S.-born preacher Anwar al-Awlaki, who reportedly had contact with three of the 9/11 bombers and was designated a "global terrorist" by American authorities in 2010.
Al-Awlaki was also suspected of having contact with Fort Hood gunman Nidal Hasan, who killed 13 soldiers at a Texas army base in 2009, and directing a failed plot to bring down a plane in Detroit in the same year.
Adebolajo was also said to have had contact with British extremist preacher Anjem Choudary, one architect of the now-proscribed group al-Muhajiroun.
Co-founder Omar Bakri Mohammed also claimed that he had spoken to Adebolajo at meetings.
The group was banned in the UK in 2010, and a study suggested that in the preceding 12 years 18 per cent of Islamic extremists convicted of terror offences in the UK had current or former links with it.
Al-Muhajiroun was recently branded "the single biggest gateway to terrorism in recent British history" in a report by campaign group Hope Not Hate.
Raised by devout Christian parents, Adebolajo said he converted to Islam in around 2002 or 2003, and his beliefs crystallised when he was in his first year studying building surveying at the University of Greenwich.
He began attending rallies, including one in 2007 when he was pictured next to Choudary, but told jurors during his trial that he later realised demonstrations made no difference.
The university has set up a panel to investigate whether Adebolajo or Adebowale were associated with it, the student union or any student societies, and if any of those bodies contributed to their extremism.
Adebowale spent time in Feltham young offenders institution, where it is claimed previous inmates were radicalised. Shoebomber Richard Reid, and Jermaine Grant, accused of plotting terror attacks in Kenya, were both held there.
He was also said to be on the periphery of the Woolwich Boys gang, and probation sources have expressed concern that teenage gang members might fall into the clutches of extremists.
Questions were also raised about the psychological effect of a murderous attack at a flat in Erith, South-East London, in which Adebowale was stabbed and his friend was killed.
Former bare-knuckle fighter Lee James was found guilty of murdering 18-year-old Faridon Alizada in 2008, and wounding Adebowale and another 16-year-old friend.
Psychiatrists suggested that Adebowale might have suffered post-traumatic stress disorder after the attack, and failed to respond to counselling.