Obama administration officials were so concerned about what would happen to key classified documents related to the Russia probe once President Trump took office that they created a list of document serial numbers to give to senior members of the Senate Intelligence Committee, a former Obama official told NBC News.

The official said that after the list of documents related to the probe into Russian interference in the U.S. election was created in early January, he hand-carried it to the committee members. The numbers themselves were not classified, said the official.

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The purpose, said the official, was to make it "harder to bury" the information, "to share it with those on the Hill who could lawfully see the documents," and to make sure it could reside in an Intelligence committee safe, "not just at Langley [CIA hq]."