One person remains in custody in wake of Westminster attack

The terrorist who killed four people outside the British Parliament building last week acted alone and his motives may never be known, United Kingdom police said.

The Prime Minister told the House of Commons this morning that the attacker was British-born and "known to MI5".

British-born Islamic convert Masood, 52, was shot dead on Wednesday after killing four people including a policeman in a rampage on Wednesday when he rammed his vehicle into pedestrians and tried to force his way into the parliament building in central London. More than 50 people of a dozen nationalities were injured, 31 of whom required hospital treatment.

In December, she said, he suddenly moved out.

A tweet from ISIS-affiliated news agency Amaq said the attacker was "a soldier" of ISIS inspired by its message. But today we meet as normal - as generations have done before us, and as future generations will continue to do - to deliver a simple message: we are not afraid. The married father of three was never convicted of any terrorism offences.

But while he added that police "need to establish with absolute clarity why he did these unspeakable acts", DAC Basu acknowledged "there is a possibility we will never understand why he did this".

Mourners pass tributes to the victims of Wednesday's attack near the Houses of Parliament in London. But she called him "a peripheral figure".

Police are investigating media reports that Masood checked his encrypted messaging service WhatsApp - or even sent a message - just before the attack, which hinted at others being involved.

"We know the threat from Islamist terrorism is very real. Our investigations and our arrests will help in that, but the public appeal will make a big difference if people come forward with more information", said Britain's top counterterrorism officer, Mark Rowley.

"Our investigation focuses on understanding his motivation, preparation and associates", he said.

In Birmingham, searches are continuing at a flat raided by armed police. Leslie Rhodes, 75, of London was named as the latest fatality on Thursday night.

Police are still trying to pin down Massod's preparation and movements before the attack.

A United Kingdom official told CNN the working theory was that the attack was ISIS "inspired or copycat". A former British army officer told the BBC that rescuers held the hand of Constable Keith Palmer and talked to him as they tried in vain to save his life after he was stabbed.

The area around Westminster, the heart of the British government since the 16th century, was teeming with Londoners and visitors when the attack began.

The killer was known to have lived recently in Birmingham. In this news special, we take a look at the man who brought terror to London.

Two of Masood's victims, Aysha Frade- a teacher in her 40s - and United States tourist Kurt Cochran, 54, died on Wednesday.

  • Joanne Flowers