US authorities believe the Afghan immigrant accused of ambushing National Guard members in Washington, DC, was not radicalized until after he came to the United States, Homeland Security Secretary Kristi Noem said on Sunday.

Speaking on NBC's "Meet the Press" and ABC’s "This Week," Noem said authorities think alleged shooter Rahmanullah Lakanwal was already living in Washington state when he became radicalized. Investigators are seeking more information from family members and others, Noem said.

Authorities identified Lakanwal, 29, as the suspect in a Wednesday shooting that took place just blocks away from the White House and which killed one National Guard member and critically wounded another. After the shooting, US President Donald Trump's administration pointed to a lack of vetting of Afghans and other foreign nationals during the term of former President Joe Biden, although Lakanwal was granted asylum under Trump.

Also Read: US stops Afghan immigration processing after National Guard ambush

Trump told reporters on Sunday his administration could pause asylum admissions into the United States for an extended period. "No time limit, but it could be a long time," Trump told reporters on Air Force One. "We have enough problems. We don't want those people."

Lakanwal entered the US in 2021 as part of the Biden administration's mass evacuation of Afghans who aided US forces during the two-decade war in Afghanistan as the Taliban took power. He was granted asylum in April by Trump's administration, a government file reviewed by Reuters showed.

Noem's comments suggest Lakanwal, who was part of a CIA-backed unit in Afghanistan, may have embraced extremism after arriving in the United States.

"We believe he was radicalized since he's been here in this country," Noem told NBC News. "We do believe it was through connections in his home community and state, and we're going to continue to talk to those who interacted with him, who were his family members."

Noem said US officials have received "some participation" so far from people who knew Lakanwal and warned the US would pursue anyone connected to the shooting.

Also Read: Ambush in US capital: National Guard member dies

"Anyone who has the information on this needs to know that we will be coming after you, and we will bring you to justice," Noem said.

After Wednesday’s attack, the Trump administration took steps to clamp down on some legal immigration, including a freeze on processing of all asylum applications.

Noem said on Sunday immigration officials would consider deporting people with active asylum cases if it was warranted.

"We are going to go through every single person that has a pending asylum claim," she said.