The terrorist behind the Westminster attack sought professional help for anger issues and told friends he dreamed of killing someone, according to reports.
Those who knew Khalid Masood, also known as Adrian Russell Ajao and Adrian Elms, said he was a "troubled" character whose volatile behaviour and violent temper caused alarm.
As investigators try to piece together his path to extremism, the Saudi embassy in London confirmed he was in the country three times.
In a statement, the embassy said he had a work visa and taught English there from November 2005 to November 2006 and again from April 2008 to April 2009. He then returned for six days in March 2015.
Masood was not tracked by Saudi security services and didn't have a criminal record there, it added.
A former friend has described how Masood put a knife against his throat in 2000 and said: "I want some blood, I want some f****** blood. I want to kill someone."
Lee Lawrence, 47, told The Daily Telegraph: "After he calmed down a bit he was saying 'What have I done? What am I doing? I am going for help, I just want blood or I want to kill someone'.
"He said he was having help, some kind of anger management."
Details of Masood's lengthy criminal history have continued to emerge since Wednesday's terrorist attack.
The 52-year-old hit pedestrians on Westminster Bridge with a car before crashing into railings outside Parliament and fatally stabbing PC Keith Palmer in the grounds of the Palace of Westminster. Three other innocent victims were killed.
Masood was shot dead by armed police moments later.
Fears are also growing he may have been groomed for extremism during his time in prison, with a childhood friend claiming the killer turned to Islam and changed his name to Khalid Masood after serving a jail term for assaulting someone with a knife.
The victim, Piers Mott, was left with a three-inch gash on his cheek and needed 20 stitches after the pub car park attack in East Sussex.
Masood's sudden religious conversion will add to concerns that criminals are being brought under the influence of hardened jihadists behind bars, something which the Government admitted was a "growing problem" last year.
Mark Ashdown told The Sun newspaper that he knew Masood under the name Adrian Elms, and described how he had changed during his time in jail.
"When he first came out he told me he'd become a Muslim in prison and I thought he was joking. Then I saw he was quieter and much more serious," Mr Ashdown said.
"There were still flashes of the old Ade, but they were few and far between.
"I heard he'd split from his partner and got even more deeply into religion. But nothing could have prepared me for hearing his name on the radio."
Two people remain in hospital in a critical condition, one with life-threatening injuries, after Masood's attack.
Scotland Yard says a 27-year-old man and a 58-year-old man who were arrested following raids in Birmingham on Thursday remain in police custody, as detectives try to determine whether Masood acted alone or was "encouraged, supported or directed" by others.
Yesterday, Sky News learned Masood had used the WhatsApp phone messaging service two minutes before he attacked, but it is unclear whether he was communicating with someone.
Detectives have seized 2,700 items, including "massive amounts" of computer data, following raids nationwide - and approximately 3,500 witnesses have talked to police.
Police have confirmed extra officers are being deployed for England's World Cup qualifier against Lithuania tomorrow.
Armed patrols will take place around Wembley Stadium, and a minute's silence will be held before kick-off at 5pm.