"An Islamist background for the crimes is likely," the Munich Prosecutor's Office said in a joint statement with Bavarian police on Tuesday, describing Monday's rampage. The perpetrator shouted "Allahu Akbar" at least two times during the incident.

He was confronted by several brave civilians, disturbing footage from the scene shows, who tried to fend him off with chairs and other objects before the police arrived. Officers shot the man in the leg and took him into custody.

The attacker was not known to the authorities as an extremist, nor on any watch lists, German media reported earlier. Nonetheless, investigators reportedly recovered Islamic State (IS, formerly ISIS) propaganda materials from the homeless shelter where he lived.

This is notable because a number of these attackers are known to intelligence services: Austrian attacker was under surveillance as known jihadist but 'mistakes' led to investigation being dropped

He has reportedly shown no remorse for his actions, telling the police he had achieved his "jihad" goals. A senior security official, Joachim Herrmann, said the suspect had been admitted to a psychiatric unit suffering mental ill health a few days prior to the attack and subsequently released.

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Carlson said that a whistleblower inside the government has warned that the NSA is surveilling electronic communications and planning to leak the material in an effort to get his show removed from the air.

"The whistleblower, who is in a position to know, repeated back to us information about a story that we are working on" which must have been procured though "my texts and emails," according to Carlson. "There's no other possible source for that information, period. The NSA captured that information without our knowledge and did it for political reasons. The Biden administration is spying on us. We have confirmed that," he said.

High-profile conservative and former New York City police commissioner Bernard Kerik called on the GOP leadership to raise the issue at the highest level.

Earlier on Monday, meanwhile, Senator Ron Wyden (D-Oregon) introduced legislation seeking to protect reporters from government surveillance, though not related to the Carlson debacle. He cited abuses under the Donald Trump administration, in which the Department of Justice targeted journalists from CNN, the Washington Post and the New York Times with probes while looking into official leaks.

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