The FBI launched three separate investigations into the leaking of classified material made public by newspaper columnist Robert Novak in the 1980s, newly obtained records show.

Previously secret FBI files reveal that the bureau pursued Novak's sources after reading columns Novak and his writing partner, Rowland Evans, published in The Washington Post in 1983 and 1987. Agents also tried to identify the source of classified information that Novak divulged in 1983 on the television show "The McLaughlin Group."

Although agents conducted interviews, reviewed appointment calendars, requested polygraph tests and even considered using an administrative subpoena to obtain phone records, they apparently were ultimately unable to confirm the identify of any of the sources.

The revelations are contained in 64 pages of files released to The Post on Wednesday in response to an open-records request filed after Novak's death in August 2009, at the age of 78. Such files become public by law after the subject of the investigation dies.

Novak, a well-known columnist and TV commentator, often was supplied with information by high-level government officials. His "Inside Report" column, which he wrote with Evans for 30 years, was widely syndicated and often used by Washington insiders as a way to surface information that could embarrass their political opponents.

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