The British Muslim shot dead during a terror attack on Parliament in March had claimed he was waging jihad in revenge against Western military action in countries in the Middle East, it emerged on Friday.
UK security services have managed to decode the last message sent out by Khalid Masood before he rammed his high- speed car into pedestrians on Westminster Bridge and stabbed to death a police officer at the gates of Parliament on March 22.
According to the Independent newspaper, the message on the WhatsApp messaging service reveals the 52-year-old Muslim convert's motivation behind the attack that claimed four innocent lives.
The person who received the message has been extensively questioned, but freed after the police and MI5 concluded that he was not part of the plot and had no prior knowledge of what was unfolding in March, the newspaper said.
Eleven others detained following the attack were freed and have been cleared from inquiries.
The insight into the terrorist's mindset follow the arrest of a suspected jihadist yesterday, just 100 yards from where Masood was shot by police, who was found armed with knives heading towards Downing Street when he was dramatically stopped by armed police.
The 27-year-old suspect was taken away by armed police and is being questioned by the Scotland Yard at a south London police station.
The access to Masood's message was achieved by what has been described by security sources as a use of “human and technical intelligence”.
Details of the method used cannot be disclosed for security reasons, but sources said they now have the technical expertise to repeat the process in future.
It was made possible because Masood's mobile telephone was recovered after he was shot dead.
Islamic State (ISIS) had claimed “credit” for his attack, but no evidence has emerged to back this up.
The issue of WhatsApp's encrypted service, which is closed to anyone besides the sender and recipient, had come under criticism soon after the attack.
“It's completely unacceptable. There should be no place for terrorists to hide. We need to make sure that organisations like WhatsApp, and there are plenty of others like that, dont provide a secret place for terrorists to communicate with each other,” UK home secretary Amber Rudd had said.
It is unclear whenRuddwas made aware that Masood's WhatsApp message had been retrieved.