London attack: Police appeal for information on Khalid Masood
Police have appealed to anyone who knew the Westminster attacker Khalid Masood to come forward with information.
Officers investigating Wednesday's attack said they wanted to hear about "associates and places he visited".
The fourth victim has been named as Leslie Rhodes, 75, from Streatham in south London - one of three killed by Masood's car on Westminster Bridge.
Masood then stabbed PC Keith Palmer near Parliament. Police said they have made two more "significant arrests".
Fifty people were injured in the attack, with 31 receiving hospital treatment. Two are in a critical condition; one has life-threatening injuries.
Updating reporters outside New Scotland Yard, Assistant Deputy Commissioner Mark Rowley said two police officers remain in hospital with "very significant" injuries.
Source: bbc.com