More details about attacker Khalid Masood's travels, confirmed by the Saudi Arabian embassy in Britain, emerged Saturday amid a massive British police effort to discover how a homegrown ex-con with a violent streak became radicalized and why he launched a deadly attack Wednesday on Westminster Bridge.
Nine people are now in custody after a woman was released on bail.
Masood attacked and killed PC Keith Palmer inside the grounds of Parliament after he ploughed into the crowds on Westminster bridge with a 4x4 vehicle.
In all, he killed four people and left more than two dozen hospitalized, including some with what have been described as catastrophic injuries.
Khan's note and flowers were placed outside of New Scotland Yard, the headquarters of the Metropolitan Police Force.
Authorities identified Masood, a 52-year-old Briton, as the man who mowed down pedestrians and stabbed a policeman to death outside Parliament in London, saying he had a long criminal record and once was investigated for extremism - but was not now on a terrorism watch list.
Two police officers injured in the attack are also in hospital with "significant injuries".
In the clip, May can be seen being directed to a waiting grey Jaguar XJ in the auto park inside the Palace of Westminster complex.
Police are still trying to pin down Massod's preparation and movements before the attack.
"The people he was hanging out with did include people suspected of having an interest in travelling to join jihadi groups overseas but the attacker himself never did so", the source said. "That understanding may have died with him", Basu added.
"However, he was known to police and has a range of previous convictions for assaults, including GBH (grievous bodily harm), possession of offensive weapons and public order offences".
The Metropolitan Police said the incident was a terrorist attack. "He seemed to be quite nice, he would be taking care of his garden and the weeds", Iwona Romek, 45, told reporters at her home.
The other victims were 48-year-old policeman Keith Palmer and, on the bridge, 43-year-old Briton Aysha Frade, who was on her way to pick up her two daughters, and an American citizen in his 50s, Kurt Cochran.
Police say there is no evidence of further attacks planned, but they are looking to find out more about Masood and whether he acted alone or was supported by anyone.
Police Officer PC Keith Palmer (48), retired window cleaner Leslie Rhodes (75), mum Aysha Frade and United States tourist Kurt Cochran (54) all lost their lives in the attack.
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