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The letter said that authorities apply for roving wiretaps in about 22 cases a year, and can do so only when the suspect is engaged in countersurveillance techniques such as frequently changing phone numbers.

The business record provision allows investigators to seize financial, medical, library and other records of a suspected terrorists.

“The absence of such an authority could force the FBI to sacrifice key intelligence opportunities,” Mr. Weich, the assistant attorney general, wrote.

The “lone wolf” provision allows authorities to monitor a person suspected of engaging in terrorism, but who may not be linked to a specific terrorist organization.