British police have made an appeal for information about Khalid Masood, the man behind the deadly terror attack in central London on Wednesday in which four people were killed and at least 20 others were injured.
Scotland Yard's top anti-terror officer Mark Rowley appealed to the public for information about Masood, who was shot dead during the attack, as London Metropolitan Police released a photo of the attacker.
Police have said that the 52-year-old had previously gone by a number of names including Adrian Elms and Adrian Russell Ajao.
Two more "significant arrests" have been made in connection with the attack and Acting Deputy Commissioner Mark Rowley said the suspects were held overnight in the West Midlands and northwest of England.
Eight other people were arrested after properties across the UK were raided following the attack.
However, six people arrested as part of the investigation have now been released from police custody, with no further police action.
The six people are: a 21-year-old woman and a 23-year-old man who were arrested at an address in Birmingham.
A 26-year-old woman and three men aged 28, 27 and 26 years old, who were arrested at separate addresses in Birmingham.
A 39-year-old woman was arrested at an address in east London on suspicion of preparation of terrorist acts. She has since been released on bail until a date in late March.
Four others remain in police custody pending further inquiries.
They include a 58-year-old man arrested yesterday morning at a separate address in Birmingham; a 27-year-old man arrested yesterday at an address in Birmingham; a 35-year-old man arrested in the early hours of this morning at an address in Manchester and a 32-year-old woman arrested this morning at a location in Manchester.
All four were arrested on suspicion of preparation of terrorist acts.
Earlier, Mr Rowley revealed that the fourth member of the public injured in the attack, who died in hospital last night, was 75-year-old Leslie Rhodes from Streatham, south London.
He said two people remain in hospital in a critical condition, one with life-threatening injuries.
Two police officers injured in the attack are also in hospital with "significant injuries".
Mr Rowley said: "We remain keen to hear from anyone who knew Khalid Masood well, understands who his associates were and can provide us with information about places he has recently visited.
"There might be people out there who did have concerns about Masood but did not feel comfortable for whatever reason in passing those concerns to us."
Masood was born with the birth name Adrian Russell Ajao, before later converting to Islam, according to reports.
Hours before carrying out his atrocity, The Sun newspaper said he stayed in the Preston Park Hotel in Brighton, telling staff as he checked out that he was going to London.
He reportedly added: "It isn't what it used to be."
Officers were seen scouring the hotel in the wake of the attack after a receipt for his stay was found in the hire car he later ploughed down pedestrians with, the paper said.
A member of staff at the hotel said last night: "We have been instructed not to talk."
Further details emerged about his violent history, which included an episode when he stabbed a man in the nose in the driveway of a nursing home in Eastbourne in 2003.
Masood ploughed a car down Westminster Bridge and stormed the Parliamentary estate armed with two blades, fatally stabbing Police Constable Keith Palmer.
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More candlelit vigils for the victims are scheduled today in Birmingham and London.
Scotland Yard said Masood - who was shot dead by police - was born in Kent on Christmas Day in 1964.
After leaving Kent, it is thought he most recently spent time in the West Midlands, with a witness to an armed raid on a flat in Edgbaston saying: "The man from London lived here."
Masood is also thought to have spent periods living in London, Sussex and Luton.
Scotland Yard said he was not the subject of any current investigations before the massacre and there was "no prior intelligence about his intent to mount a terrorist attack".
But he was known to police and MI5 and had convictions for assaults, including grievous bodily harm, possession of offensive weapons and public order offences.
His victims on Westminster Bridge included a US tourist from Utah who was celebrating his wedding anniversary and a "highly regarded and loved" staff member of a local college.
Kurt Cochran and his wife Melissa, on the last day of a trip celebrating their 25th anniversary, were visiting her parents, who are serving as Mormon missionaries in London. Mrs Cochran was badly injured.
Aysha Frade, who worked in administration at independent sixth-form school DLD College London, in Westminster, is understood to have been 43 and married with two daughters.
A house in Carmarthenshire, south west Wales, was also searched, Dyfed-Powys Police said.
British Prime Minister Theresa May said Masood was investigated some years ago in relation to concerns about violent extremism but was a "peripheral figure".
British Home Secretary Amber Rudd defended the security and intelligence agencies, saying: "The fact that he was known to them doesn't mean that somebody has 24-hour cover."
Meanwhile, President Michael D Higgins was at the British embassy to sign the book of condolence for the four victims of the Westminster attack, which he has described as an appalling criminal act.
