Live updates: Westminster attack investigation
Police and intelligence agencies are mounting a massive investigation to establish what led Khalid Masood to carry out the attack on Westminster.
There have also been calls for security services to get access to encrypted messages such as WhatsApp after it emerged that Masood used the messaging service moments before the attack.
Here is the latest on what we know:
- Police have arrested a 30-year-old man in Birmingham in connection with the attack
- Another man of 58 who was arrested on Thursday remains in custody
- Scotland Yard have said the attack was over in just 82 seconds
- They believe Masood acted alone and it may never be known why he did it
- Masood ploughed a Hyundai i40 across Westminster Bridge and stormed the Parliamentary estate armed with two knives, fatally stabbing Pc Keith Palmer before being shot dead by police
- Three other innocent people died in the attack on Wednesday
