Seven of the 11 people arrested since the London attack have been released with no further action, police have said.
Two men remain in custody, while two women have been released on bail until late March, the Metropolitan Police said.
Police are trying to establish whether attacker
Khalid Masood acted alone.
Meanwhile, the Saudi Arabian government has confirmed that Khalid Masood worked in the country as an English teacher in two different spells between 2005 and 2009.
Four people were killed and 50 injured after
Khalid Masood drove his car into people on Westminster Bridge and stabbed an officer guarding Parliament.
Officer Keith Palmer, 48, died of his wounds. Khalid Masood was shot dead by police.
Police said their investigation into the attack would focus on Khalid Masood’s “motivation, preparation and his associates”.
On March 24, Metropolitan Police Assistant Deputy Commissioner Mark Rowley said officers would investigate whether
Khalid Masood “acted totally alone inspired by terrorist propaganda, or if others have encouraged, supported or directed him”.
Image source Met Police
The Saudi Arabian embassy in London said Khalid Masood had been in the country from November 2005 to November 2006 and April 2008 to April 2009, when he worked as an English teacher.
In 2015, Khalid Masood obtained an Umra visa – allowing pilgrimage to Mecca – and was in the country from March 3 to 8.
The embassy said:
“The Kingdom of Saudi Arabia strongly condemns Wednesday’s terrorist act in London, as it does all forms of terrorism.
“The attack in London this week has again demonstrated the importance of international efforts to confront and eradicate terrorism.”
Two of Khalid Masood’s victims, Aysha Frade – a teacher in her 40s – and US tourist Kurt Cochran, 54, died on March 22.
Retired window cleaner Leslie Rhodes, 75, from Clapham, south London, died on March 23 when his life support machine was turned off.
Fifty people were injured in the attack, with 31 receiving hospital treatment. Two are in a critical condition, and one has life-threatening injuries.
Two officers remain in hospital with “very significant” injuries, one of whom has been identified as Officer Kristofer Aves.
VIDEO London police has named Khalid Masood as the man believed to have carried out the terror attack in Westminster.
The 52-year-old, who was shot dead by police, had not been the subject of any current police investigations, but had a range of previous convictions.
Khalid Masood was believed to have been living in the West Midlands.
ISIS has said it was behind the attack, in which Officer Keith Palmer, Aysha Frade and American tourist Kurt Cochran were killed.
Five men and three women were arrested in London and Birmingham on suspicion of preparation of terrorist acts following March 22 attack.
Police says detectives are continuing to search a number of addresses, including one in Carmarthenshire, three in Birmingham and one in east London. Addresses in Brighton and south-east London have also been searched.
Image source NBC News
Khalid Masood drove into pedestrians on Westminster Bridge before crashing his car into railings and then running into the grounds of Parliament, armed with a knife.
He stabbed Officer Keith Palmer before being shot dead.
Police said there had been no prior intelligence about Khalid Masood’s intention to carry out an attack.
However, he was known to the police and his previous convictions included causing grievous bodily harm, possession of offensive weapons and public order offences.
Khalid Masood’s first conviction was in November 1983 for criminal damage and his last in December 2003 for possession of a knife.
He had not been convicted of any terrorism offences.
Scotland Yard said Khalid Masood “is not at this early stage believed to be his birth name” and that research into his aliases was being carried out.
Car rental company Enterprise said the vehicle used in the attack had been rented from its Spring Hill depot in Birmingham.
VIDEO Seven people have been arrested in raids following London attack that left four dead, police have said.
Acting Deputy Commissioner and Head of Counter Terrorism Mark Rowley said hundreds of detectives have worked through the night, carrying out searches at six addresses.
Those who died were a woman in her 40s, a man in his 50s, police officer Keith Palmer and the attacker, he said.
Seven of the injured are still in hospital in a critical condition.
A further 29 had been treated in hospital, Mark Rowley added.
Image source Reuters
In the attack on March 22, a man
drove a car along a pavement in Westminster knocking down pedestrians, leaving dozens injured.
He then stabbed a policeman and was shot dead by police in the grounds of Parliament.
In a statement made outside Scotland Yard, Mark Rowley said:
“The inquiries in Birmingham, London and other parts of the country are continuing.
“It is still our belief – which continues to be borne out by our investigation – that this attacker acted alone and was inspired by international terrorism.
“To be explicit, at this stage we have no specific information about further threats to the public.”
Mark Rowley said he would not name the bridge victims yet, who were “a mix of nationalities”, and urged journalists not to publish the attacker’s name while searches were continuing.
He said Londoners should expect to see more police officers on the streets, after officers’ leave had been cancelled and duty hours extended.
It was initially thought that three members of the public had been killed on Westminster Bridge, but Mark Rowley referred to just two in his statement.
A woman has been killed on Westminster Bridge in central London in what police are treating as a terrorist incident.
A police officer was also stabbed in the nearby Houses of Parliament by an attacker, who was shot by police.
The attacker struck several pedestrians as he drove a car across the bridge, before crashing it into railings.
Image source NBC News
A number of other people were hurt – some with “catastrophic” injuries – a doctor at St Thomas’ Hospital said.
Lawmakers said they had heard three or four gunshots and staff inside Parliament were told to stay inside their offices.
A Downing Street source said PM Theresa May was safe.
Theresa May was seen being ushered into a silver Jaguar car as what sounded like gunfire rang out at Parliament during the incident.