Police officials said on Monday there was no indication the man who killed four people in London last week was associated with the so-called "Islamic State" or al Qaeda jihadist groups.

Deputy Assistant Commissioner of the Metropolitan Police Neil Basu told reporters that British-born Islamic convert Khalid Masood, 52, clearly had "an interest in jihad," but doubted he discussed plans of an attack with others. On Sunday Basu revealed that police believe Masood likely acted alone and that there was no intelligence to suggest further attacks were planned.

The self-styled "Islamic State" group (IS) had claimed responsibility for the attack, while police inquiries since have concentrated on whether Masood was acting with accomplices.

Basu, who also serves as the UK's national coordinator for counter-terrorism, said the nature of Wednesday's attack - in which Masood ran over pedestrians on a London bridge before fatally stabbing a police officer - appeared to be based on "low-sophistication, low-tech, low-cost techniques copied from other attacks." He was shot dead by police forces shortly after. 

Police are reportedly 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.

Masood's mother 'saddened and numbed'

Masood's mother Janet Ajao issued a statement through the police on Monday saying she was "deeply shocked, saddened and numbed" by her son's murderous rampage.

"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 said.

"I know when, where and how Masood committed his atrocities, but now I need to know why," Basu said, adding that he was not radicalized during one of his stints in jail, the last of which was in 2003. "Most importantly, so do the victims and families."

'We may never know'

"We must all accept there is a possibility we will never understand why he did this. That understanding may have died with him," Basu added.

Two people remain in custody for questioning, neither of whom have reportedly been charged or identified. Both were reportedly questioned on Monday.

Nine others who had been arrested in connection with the investigation have been released. Of them, two men, one aged 58, and the other 27 - both arrested in Birmingham - are being held under the Terrorism Act. Two women have been released on bail, a 32-year-old arrested in Manchester and a 39-year-old from London.

Misjudged threat

Masood had been considered by intelligence officers to be a known criminal who posed little serious threat.

He had shown up on the periphery of previous terrorism investigations that brought him to the attention of Britain's MI5 spy agency.

Masood taught English in Saudi Arabia from November 2005 to November 2006 and again from April 2008 to April 2009, a Saudi Embassy statement released late Friday said.

Details about how he became radicalized aren't clear. 

Eighty-two seconds

Having reconstructed the attack, the police said it had begun at 14:40:08 when Masood's hire car mounted the pavement on Westminster Bridge, weaving along the footpath and road until 14:40:38 when he crashed into the perimeter fence of the Palace of Westminster.

He left the car at 14:40:51 and was shot by a police firearms officer, part of the close protection team of the defense secretary Sir Michael Fallon, in the palace courtyard at 14:41:30.

At 14:40:59, the first call to emergency services was made to report the incident.

jbh, dm/gsw (Reuters, AP)