Newly declassified FBI documents show that the government deliberately concealed evidence and allowed the conviction of a civil liberties activist in one of the most important cases to come out of the McCarthy era, the Los Angeles Times reported Friday.

The American Civil Liberties Union and the law firm of Loeb & Loeb filed a court petition Thursday to set aside the 1959 contempt-of-Congress conviction of civil rights activist Frank Wilkinson.Wilkinson was sent to jail for refusing to tell the House Committee on Un-American Activities whether or not he was a member of the Communist Party.

A team of civil rights lawyers now say they have uncovered evidence that the FBI knew that the only witness against Wilkinson could not be believed when her testimony was used to convict him, the Times said.

After exhausting several appeals that went all the way to the U.S. Supreme Court, Wilkinson served nine months of a one-year prison term in 1961.

When government documents of the case became declassified last year, Wilkinson's lawyers found a 1961 FBI memorandum reporting that the witness, Anita Schneider, "exhibited emotional instability" at a hearing in 1956.

The memorandum also admitted that information on Wilkinson's alleged Communist Party membership therefore "comes from a source not considered advisable to use as government witnesses."

Schneider testified before the committee, saying that during her membership in the Communist Party from 1951 to 1955, she knew Wilkinson to have also been a member.