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The family members of the two San Bernardino killers, Syed Farook and Tashfeen Malik, could be criminally liable if they withheld information, Judge Andrew Napolitano said on "The Kelly File" tonight.

Judge Napolitano explained that it is not a crime to fail to report somebody else's crime in the U.S., but there is an exception for treason.

"Treason, which is defined as waging war on the United States or giving aid and comfort to the United States' enemies in wartime," Judge Napolitano said. "You could argue that these two killers waged war on the United States."

He asserted that it's worth the FBI going down that street to find out what family members of the couple knew, because it's likely to lead to other people.

"It is worth charging [Farook's mother], if for no other reason than to induce her to cough up who else probably knew about this," Judge Napolitano said.

He added, however, that the charge of treason will be a very high bar to clear for a potential prosecutor.

"We don't live in a society where you report everything - that results in too many false reports," Judge Napolitano said. "But we do live in a society where you can be prosecuted for failing to report treason."

Watch more above.

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