Westminsiter attacker was using WhatsApp minutes earlier, police probe possibility of wider network
The London attacker used WhatsApp just two minutes before he ploughed his car into pedestrians, leading police to investigate a possible wider extremist network.
Khalid Masood was active on the encrypted messaging service at 2.37pm on Wednesday, although it remains unclear whether the 52-year-old was sending, receiving or simply viewing messages.
Investigators believe he was inspired by Islamist terrorism and Isil has claimed responsibility for the massacre that left four victims dead, although the extent of the group's involvement is not yet known.
Scotland Yard's Deputy Commissioner, Mark Rowley, said police were probing whether Masood acted completely alone after being inspired by terrorist propaganda or was "encouraged, supported or directed" by others.
Nikita Malik, a senior researcher at the Quilliam Foundation, said WhatsApp and social media had been used for a variety of purposes by Isil-inspired terrorists.
"In a lot of other incidents people have shared material," she told 'The Independent'. "It can act as a sort of a modern suicide note to explain their justification."
Meanwhile, Mr Rowley said more "significant" arrests had been made yesterday, bringing to 10 the number of people in custody over the attack, which killed four people and the assailant.
The latest arrests were a man and a woman detained early yesterday in Manchester.
Detectives have searched 21 properties in London, Brighton, Wales, Manchester and Birmingham in one of Britain's biggest counter-terrorism operations in years.
"We've seized 2,700 items from these searches, including massive amounts of computer data for us to work through," Mr Rowley said, adding that contact had been made with 3,500 witnesses.
An American man from Utah, a British retiree and British female school administrator were killed on the bridge, and police officer Keith Palmer was stabbed to death.
The latest victim, a man who died in hospital on Thursday night, was named as 75-year-old Leslie Rhodes from London.
Meanwhile, President Michael D Higgins and Taoiseach Enda Kenny signed a book of condolence at the British embassy in Dublin for the victims.
The President expressed his solidarity to British ambassador Dominick Chilcott, saying it is very important to see the atrocity as a criminal act.
Mr Higgins also said he would be writing to Queen Elizabeth.