London(CNN) The mother of Khalid Masood said she is "deeply shocked, saddened and numbed" by the attack last week by her son that left four people dead in London.
Masood rammed a car into pedestrians on Westminster Bridge, killing three people and leaving dozens injured. He crashed the vehicle before fatally stabbing an on-duty police officer on the grounds of Parliament. Officers shot Masood, 52, dead.
"Since discovering that it was my son that was responsible, I have shed many tears for the people caught up in this horrendous incident," mother Janet Ajao said in a statement released Monday.
"I wish to make it absolutely clear, so there can be no doubt, I do not condone his actions nor support the beliefs he held that led to him committing this atrocity."
London Metropolitan Police say they don't believe Masood was directed by ISIS or al Qaeda.
Masood's deadly rampage "appears to be based on low-sophistication, low-tech, low-cost techniques copied from other attacks, and echo the rhetoric of (ISIS) leaders in terms of methodology and attacking police and civilians," Deputy Assistant Commissioner Neil Basu said Monday.
"But at this stage I have no evidence he discussed this with others," he said.
Authorities are investigating how Masood, who used multiple aliases, apparently became radicalized. He was born Adrian Russell Ajao but also used the name Adrian Elms, police have said.
Born in Kent, Masood had previous convictions, including some for violent offenses but none for terrorism, police said. His most recent conviction was in 2003 for possession of a knife.
Basu urged anyone who had contact with Masood in the days, weeks or months leading up to the attacks to reach out to police.
American tourist Kurt Cochran, British citizen Aysha Frade and police constable Keith Palmer died in the attack Wednesday.
A fourth victim, 75-year-old Leslie Rhodes of south London, died Thursday night after his life support was withdrawn, police said.
Cochran and his wife, Melissa, were visiting London to celebrate their 25th wedding anniversary when Masood plowed his car into pedestrians on Westminster Bridge. Melissa Cochran, suffered a broken leg, a broken rib and a cut to her head, but she will recover from her injuries, her brother Clint Payne said on social media.
Frade was an administrator at DLD College London.
"She was highly regarded and loved by our students and by her colleagues," Principal Rachel Borland said in a statement.
Palmer has been called a hero since he was killed in the line of duty.
"Keith Palmer was killed while bravely doing his duty, protecting our city and the heart of our democracy from those who want to destroy our way of life," London Mayor Sadiq Khan said.
Palmer was much more than a dedicated officer, his family said in a statement.
"He will be remembered as a wonderful dad and husband. A loving son, brother and uncle. A long-time supporter of Charlton FC," his family said.