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Story highlights

Such findings seem to undercut the Trump administration's case for its travel ban

The assessment is based on "unclassified, open source materials"

(CNN) —  

A recent Department of Homeland Security intelligence assessment found that most foreign-born violent extremists do not arrive in the US radicalized, but become radicalized after living in the US for several years.

Such findings seem to undercut the Trump administration’s case for its travel ban and track with other studies, including one by the New America Foundation, that find no clear connection with violent attacks or attempts in the US and travel from certain countries.

Work on the assessment, which was first reported by MSNBC Thursday night and confirmed by a DHS spokesman to CNN Friday morning, began in August. It is based only on “unclassified, open source materials, including a Department of Justice list of unsealed cases. It does not include information from historical or current investigative case data or current intelligence or threat stream data from classified data sets.”

DHS said the assessment is “used to inform federal, state, local, tribal, and territorial counterterrorism, law enforcement, and countering violent extremism officials, as well as immigrant screening and vetting officials on trends of foreign-born individuals engaged in terrorism activity in the homeland.”

The report examined 88 cases.

CNN has reached out to the White House for comment.

In his address to Congress Tuesday night, President Donald Trump stated, “According to data provided by the Department of Justice, the vast majority of individuals convicted for terrorism-related offenses since 9/11 came here from outside of our country.”

Those figures, however, have been challenged by independent researchers.

“Trump’s allegation that the ‘vast majority of individuals convicted for terrorism-related offenses since 9/11 came here from outside our country’ is inaccurate,” Karen Greenberg, the director of the Center on National Security at Fordham Law, which maintains a database on US terrorism cases, told CNN.

“In fact, according to statistics compiled by the Center on National Security at Fordham Law, of the nearly 500 cases related to ISIS, al Qaeda and associate forces since 9/11, just under 50% of those convicted were born outside the United States,” she continued. “And for the ISIS-related cases – which represent nearly 90% of today’s terrorism cases – only one-third of those convicted (and 42% of those charged with terrorism or killed during an attempted attack) were born outside the United States.”

CNN’s Theodore Schleifer and Paul Cruickshank contributed to this report.