Authorities can't see what was sent because WhatsApp encrypts all messages to ensure users' privacy. Video provided by Newsy Newslook

Police have released an image of Westminster attacker Khalid Masood.

The people gathered in Trafalgar Square stood together quietly, respectfully, flanked by police officers with the rumble of helicopters a constant presence above.

His wife is in hospital, after suffering a broken leg and rib.

THE terrorist police behind the London attacks has been named as Khalid Masood, 52.

The London terrorist attacker has been named by police as Khalid Masood.

Islamic State (IS, formerly ISIS/ISIL) has claimed responsibility for the attack outside the UK parliament on Wednesday which left four people dead, according to the terror group’s news agency Amaq.

British Prime Minister Theresa May on Thursday said police have identified the Westminster attack suspect as a British-born man who was already known to the country’s intelligence services.

WARNING: Graphic content