The UK family of Lee Rigby say they hold Facebook partly responsible for his murder, after a report found an internet company failed to take action over an online chat in which one of the killers vowed to slay a soldier.
The Intelligence and Security Committee's long-awaited report on Tuesday labelled an unnamed internet company, widely reported to be Facebook, a "safe haven for terrorists" because it did not flag up the online exchange between Michael Adebowale and a foreign jihadist, which took place five months before Fusilier Rigby's murder.
Muslim converts Michael Adebolajo and Adebowale used a car to run down Fusilier Rigby in south east London in May 2013, before savagely attacking the defenceless soldier as he lay in the road.
The parliamentary watchdog's chair Sir Malcolm Rifkind stated that the web firm could have made a difference by raising the conversation, and said there was "a significant possibility that MI5 would have been able to prevent the attack" as Adebowale would have become "a top priority".
"Facebook have my brother's blood on their hands," Fusilier Rigby's sister Sara told the Sun newspaper.
"I hold them partly responsible for Lee's murder."
Fusilier Rigby's stepfather Ian said the social networking site failed the family when they failed to alert authorities.
A Facebook spokesman said the company was horrified by the murder.
"We don't comment on individual cases but Facebook's policies are clear, we do not allow terrorist content on the site and take steps to prevent people from using our service for these purposes," he said.
Fusilier Rigby's family later told Good Morning Britain the report had left them with "a lot of questions".
Mr Rigby said internet companies have a duty of care towards their customers and should pass information on when necessary.
He said he would like to put his questions to Prime Minister David Cameron, including why there was a delay in information being passed to intelligence agencies.
"He's the only one that has the full report and he's probably the only one that could get the answers that we want," he said.
A number of online accounts owned by Adebowale were automatically disabled due to association with terrorists and terrorism - but the unnamed web firm was unaware as it does not manually review such decisions, and it did not notify law enforcement agencies.
Adebowale was in contact with an extremist now known to have links to al Qaeda in the Arabian Peninsula (AQAP) in late 2012, the report said, however this was not revealed until an unidentified third party notified government intelligence after the attack.
The group of MPs said in their report that it was "highly unlikely" the intelligence agencies would have seen the discussion, which came to light only after the barbaric murder near Woolwich barracks on May 22 last year, without the company's help.
