The attacker who plowed a vehicle through a throng of pedestrians and then stabbed a policeman outside Britain's parliament was named on Thursday as Khalid Masood, a British-born man who was once investigated by MI5 intelligence officers over concerns about violent extremism.
In the attack, British-born Khalid Masood drove a auto into people on Westminster Bridge near the British parliament, before stabbing police Constable Keith Palmer.
Six people arrested after the attack on Westminster have been released, while four are still in custody, Scotland Yard says. Then he jumped out and attacked police officer Keith Palmer, who was guarding Parliament, fatally stabbing him before being shot dead by police.
Meanwhile, the Islamic State group has said it was behind the attack. His most recent conviction was in 2003 for possession of a knife. Five people, including the attacker died, while at least 50 other people were injured.
One of the ten others who were released, a 32-year-old woman, is on bail - the others have all been freed with no further action, according to a Metropolitan Police statement.
We have to remember that the person who did this is no more representative of British Muslims than the person who killed Jo is representative of people that are from Yorkshire.
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"Our investigation focuses on understanding his motivation, his operation and his associates", Rowley said.
Nine people remain in custody on suspicion of preparing terrorist acts.
Currently, the detectives are searching two addresses in Birmingham and one in east London on Friday afternoon as the investigation grows.
Seven people are in a critical condition, and 29 have been treated in hospital.
Meanwhile, police are trying to work out if anyone else knew what Khalid Masood planned to do. "I'm confident that we are doing all that we can to keep our city safe, to keep Londoners safe and to keep visitors safe", he said.
On Thursday, hundreds gathered to hold a vigil to pay tribute to the victims of the attack. Extra police officers will be patrolling London, he said. Our acting commissioner, Craig Mackey, told thousands who gathered in central London last night terrorist have tried to tear this city apart before and they have never succeeded.