Khalid Masood, the Westminster attacker, had a clear interest in jihad and his methods echoed the rhetoric of Islamic State leaders, Scotland Yard has said.

Six days into the investigation, the Metropolitan police’s deputy assistant commissioner Neil Basu, who is also senior national coordinator for UK counter-terrorism policing, said there was no evidence that Masood had discussed the planning of his attack with others.

But he made clear that the attacker’s communications on 22 March – when he drove a car into pedestrians on Westminster Bridge and fatally stabbed a police officer guarding the Palace of Westminster, killing four people in total – are the main line of enquiry.

Masood’s phone was reported to have connected with the encrypted messaging app WhatsApp just before the attack.

The Met’s comments came as Masood’s mother, Janet Ajao, broke her silence, saying she was “shocked, saddened and numbed by the actions my son has taken that have killed and injured innocent people in Westminster”.

Masood was shot dead by a protection officer in the courtyard of the Palace of Westminster. His attack claimed the lives of PC Keith Palmer, Kurt Cochran, an American tourist, Aysha Frade, an administrator at a London sixth form college, and Leslie Rhodes, a 75-year-old window cleaner.

Since the attack, Ajao, 69, has been living under armed police guard in west Wales where she runs a craft business.

“Since discovering that it was my son who was responsible, I have shed many tears for the people caught up in this horrendous incident,” she said. “I wish to make it absolutely clear, so there can be no doubt, I do not condone his actions or support the beliefs he held that led to him committing this atrocity.”

In a public appeal for people who were in contact with Masood to give evidence, Basu said: “If you heard from him on 22 March, please come forward now. The information you have may prove important to establishing his state of mind.

“His attack method appears to be based on low sophistication, low tech, low cost techniques copied from other attacks, and echoes the rhetoric of Islamic State leaders in terms of methodology and attacking police and civilians but, at this stage, I have no evidence he discussed this with others.

Police officers stop to look at floral tributes to the victims of the 22 March terror attack in Westminster. Photograph: Justin Tallis/AFP/Getty Images

“There is no evidence that Masood was radicalised in prison in 2003, as has been suggested. This is pure speculation at this time. Whilst I have found no evidence of an association with Islamic State or al-Qaida, there is clearly an interest in jihad.”

Scotland Yard confirmed that he had changed his name from Adrian Ajou to Khalid Masood in 2005. At that time, he had just married Farzana Malik, a Muslim marketing assistant in Medway, Kent.

A school friend, Mark Ashdown, 52, has said that he became a Muslim while in prison.

After two spells teaching English in Saudi Arabia he moved to Luton, Bedfordshire, in about 2009 and lived at addresses in the Bury Road area of the town, near to several radical Islamists and where the subsequently banned group al-Muhajiroun was active. In 2010, he became known to the security services as a potential extremist.

On Sunday, there were unconfirmed reports that Masood may have shown up on MI5’s radar during an investigation into a plot by several Luton men to blow up an army base using a remote-controlled car. Four men were jailed in 2013 over the plot against a Territorial Army centre in Luton.

However, Basu said that as Masood’s last criminal offence took place in 2003 “he was not a current subject of interest or part of the current domestic or international threat picture for either the security service or counter-terrorism policing”.

He added: “I know when, where and how Masood committed his atrocities, but now I need to know why. Most importantly, so do the victims and families.”

Earlier, outside Scotland Yard, Clint Payne, a spokesman for the Cochran family, said that Kurt Cochran’s wife, Melissa, who was injured in the attack was “steadily improving and she has been strengthened by the presence of her family”, who had travelled from the US.

“The most difficult part of all of this is that Kurt is no longer with us and we miss him terribly,” Payne said. “He was an amazing individual who loved everyone and tried to make the world a better place. He left a legacy of generosity and service that continues to inspire us.”

The evidence that Masood was using WhatsApp just before the attack sparked a debate over authorities’ capacity to intercept suspects’ communications as part of national security investigations.

Lord Carlile, the former independent reviewer of terrorism legislation, said encryption presented security services with a “considerable” problem. He said he hoped new legislation would not be needed but added that it may have to be considered if service providers did not cooperate.

WhatsApp said it was “co-operating with law enforcement as they continue their investigations”.

An inquest for the four victims will open and adjourn on Wednesday at Westminster coroner’s court, while Masood’s inquest will open on Thursday.