London terror attacker used WhatsApp, the encrypted messaging app, before rampage

Police in London on Monday said communications sent by Khalid Masood just before last week's terrorist rampage are "a main line of enquiry" as they piece together the case.

Masood sent a WhatsApp message to an unknown person prior to the attack, authorities said Sunday, but the message’s contents — and its intended recipient — can't be accessed by police because the popular messaging service encrypted them.

In a statement, Neil Basu, senior national coordinator for UK Counter Terrorism Policing, asked anyone who heard from Masood on March 22 to "please come forward now." Any information about communications with Masood "may prove important to establishing his state of mind," he said.

Masood used WhatsApp, which is owned by Facebook, just minutes before the attack that left three pedestrians and one police officer dead and dozens more wounded, The Associated Press reported.

WhatsApp said in a statement that the company was "horrified at the attack" and was cooperating with the investigation.

Police have arrested 12 people in the investigation, including a 30-year-old man who was detained in Birmingham on Sunday on suspicion of preparing terrorist acts, the BBC reported. Masood lived in Birmingham.

Nine people arrested after the attack have been freed without charges, while one person was released on bail, AP reported.

Basu said on Monday that Masood's attack method "appears to be based on low sophistication, low tech, low cost techniques copied from other attacks, and echo the rhetoric of (Islamic State) leaders in terms of methodology and attacking police and civilians."

But he said that at this state of the investigation, "I have no evidence he discussed this with others."

He also said there's no evidence that Masood, who was imprisoned in 2003, was radicalized in prison. He also said that while there was no evidence of any association between Masood and ISIS or al-Qaeda, "there is clearly an interest in jihad."

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Appearing on BBC and Sky News on Sunday, Britain’s Home Secretary, Amber Rudd, urged WhatsApp and other encrypted services to make their platforms accessible to intelligence services and police as they try to find out more about the attacks.

“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,” she said.

Masood drove a rented SUV into pedestrians on Westminster Bridge before smashing it into Parliament’s gates and rushing onto the grounds, where he fatally stabbed a policeman and was shot by other officers. A detailed police reconstruction found that the entire attack lasted 82 seconds. Scotland Yard has said it believes Masood, 52, acted alone.

Police are trying to pinpoint his motive and identify any possible accomplices, making the WhatsApp message a potential clue to his state of mind and social media contacts.

Britain’s Telegraph reported that cybersecurity experts were expected to employ their own hackers to access the message.

Rudd said she would be meeting technology firms this week, adding that encryption that conceals a terrorist’s actions is “completely unacceptable — there should be no place for terrorists to hide.”

The company, which has a billion users worldwide, has said protecting private communication is one of its "core beliefs."

Basu said it may never be possible to fully determine Masood’s motives.

“That understanding may have died with him,” Basu said. . “Even if he acted alone in the preparation, we need to establish with absolute clarity why he did these unspeakable acts, to bring reassurance to Londoners.”

The Islamic State, which is losing territory in Iraq and Syria but still has radical followers in other parts of the world, has claimed Masood was a “soldier” carrying out its wishes to attack Western countries.

Masood spent time in prison for violent crimes in the U.K. He also worked in Saudi Arabia teaching English for two years and traveled there again in 2015 on a visa designed for religious pilgrimages.

Contributing: AP.

Follow Greg Toppo on Twitter: @gtoppo