The CIA and FBI are looking for the person responsible for leaking top-secret material detailing CIA tools for surveilling smartphones and other devices, CBS News reported Wednesday.

The leaker is believed to be an agency insider, CBS News reported, citing sources familiar with the probe. The manhunt is part of a joint agency investigation into a massive security breach that led to the release of thousands of documents by the website WikiLeaks.

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Many of the documents were held in a highly secure part of the CIA, meaning that the leaker would most likely have to be someone in the agency. But hundreds of agency employees and contractors are said to have had access to the documents.

Investigators are beginning to comb through those names.

WikiLeaks said in a statement that it had obtained the material from a former contractor.

The CIA has not confirmed whether the material released by WikiLeaks is authentic, though it has not denied its authenticity either.