The Latest on London attack investigation (all times local):
The mother of Westminster attacker Khalid Masood says she is "deeply shocked, saddened and numbed" by his murderous actions.
In a statement released through the police, Janet Ajao says that "since discovering that it was my son that was responsible, I have shed many tears for the people caught up in this horrendous incident."
Ajao says she wants to make it "absolutely clear" that she does not condone his actions or support the beliefs that led him to carry out the attack.
Masood was born in southern England in 1964 as Adrian Elms, and took the name Adrian Ajao after his stepfather, whom his mother married when he was a small child. Police say he changed his name to Khalid Masood in 2005.
Janet Ajao lives in rural Wales.
A senior British counterterrorism officer says police have found "no evidence" Westminster attacker Khalid Masood was associated with the Islamic State group or al-Qaida.
Deputy Assistant Commissioner Neil Basu says Masood clearly had "an interest in jihad," but police have no evidence he discussed his attack with others.
Basu says in a statement that the attack in which Masood used an SUV and knives to kill four people in London "appears to be based on low sophistication, low tech, low cost techniques copied from other attacks."
He says Masood was not a "subject of interest" for counterterror police or the intelligence services before last week's attack.
The family of an American man killed last week in the London attack has offered tribute to his generosity and say they are grateful for the help and support so many have shown during a horrible time.
Kurt W. Cochran from Utah was on the last day of a European trip celebrating his 25th wedding anniversary when he was killed on Westminster Bridge. They were visiting her parents, who are serving as Mormon missionaries in London.
Family spokesman Clint Payne told reporters Tuesday that Cochran's wife, Melissa, is steadily improving.
Payne says the most difficult aspect of the experience has been that "Kurt is no longer with us, and we miss him terribly."
Payne says that Cochran "left a legacy of generosity and service that continues to inspire us."
British police say that two people remain in custody following last week's attack in London as messaging services face criticism for encrypted networks that allow attackers to communicate in secret.
Attacker Khalid Masood is believed to have used the messaging service WhatsApp before running down pedestrians on Westminster Bridge and storming a gate outside Parliament armed with two knives. Four died in the rampage, including a police officer.
Encryption makes it more difficult to know whether Masood was acting with an accomplice. Britain's Home Secretary Amber Rudd wants technology companies to do more to make it possible for security services to have access to such messages.
Police say that a 30-year-old man arrested in Birmingham on Sunday and a 58-year-old man arrested shortly after the attack remain in police custody.
The European Union's presidency says people's privacy must be protected following British calls for police access to encrypted messages in case of attacks.
Maltese Interior Minister Carmelo Abela said Monday "there is a fine line here. We need to of course protect the privacy of the people but we also have to protect the security of the people."
British Home Secretary Amber Rudd said Sunday that "we need to make sure that organizations like WhatsApp — and there are plenty of others like that — don't provide a secret place for terrorists to communicate with each other."
London attacker Khalid Masood sent a WhatsApp message that can't be accessed because it was encrypted.
Abela said that EU states and internet providers should continue talks to establish the right security-privacy balance