A U.S. Senate panel has released half-century old records of controversial hearings led by former Senator Joseph McCarthy into alleged communist infiltration of U.S. institutions. The documents shed light on a dark chapter in American history.

Senator McCarthy was chairman of the Senate Permanent Subcommittee on Investigations in 1953 and 1954 at the height of the Cold War between the United States and the Soviet Union.

The Wisconsin Republican used his position to wage a relentless anti-communist campaign, denouncing public figures and holding a series of highly confrontational hearings that his critics denounced as a "witch hunt."

With little, if any, proof of his accusations, Senator McCarthy relied on slander and innuendo to tarnish his opponents' reputations, a practice that has come to be known as "McCarthyism."

On Monday, the very subcommittee that he chaired released the transcripts from those hearings, including more than 9,000 pages of testimony from more than 500 witnesses in 160 closed-door sessions.

"The transcripts, which have been sealed for 50 years, shed new light on a shameful chapter in American history," said Senator Susan Collins, the Maine Republican who oversaw the project, "a time when hundreds of innocent people were paraded before a Senate subcommittee, with little regard for due process or their constitutional rights, a time when character assassination, mud-slinging, and guilt by association trumped the truth and fairness."

Senator Collins spoke in the room where many of the hearings took place.

Among the witnesses Senator McCarthy had subpoenaed were composer Aaron Copland, writer Langston Hughes, and New York Times journalist James Reston. There were also actors, government employees, labor organizers and army officers.

While Senator McCarthy told witnesses of their constitutional right to decline to answer a question, he interpreted any refusal to do so as an admission of guilt.

Although the senator threatened witnesses with contempt of Congress or perjury charges if they did not testify, not one person went to prison as result of the hearings.

"Either the Justice Department refused to prosecute, or the courts threw the cases out, or in the very few cases where people were convicted, all of the convictions were overturned," said Don Ritchie, a Senate historian.

In 1957 the Supreme Court ruled that witnesses before congressional committees have full constitutional rights. The Senate also revised its rules to prevent future abuses.

But Senator Collins says the newly released documents offer an important reminder. "Today, by providing broad public access to the transcripts from this era, we hope that the excesses of McCarthyism will serve as a cautionary tale to future generations," she said.

While no witness was imprisoned in connection with Senator McCarthy's hearings, one man, a Voice of America employee, did lose his life.

Senate historian Donald Ritchie says Raymond Kaplan, a VOA engineer, committed suicide because he was afraid he was going to be called as a witness.

"He was not called, but others who worked with him, this was in the Voice of America, were called to explain what had happened. It was in this atmosphere of fear that he was sure that he was going to be targeted by the subcommittee," said Mr. Ritchie.

At issue, were two transmitters that Mr. Kaplan had a role in building. The towers did not transmit signals to the Soviet Union as they were meant to do, and Senator McCarthy was convinced that this was a result of subversion, not an honest mistake, as was later shown.

Historian Ritchie says Mr. Kaplan threw himself in front of a truck in Cambridge, Massachusetts, in March 1953, leaving a poignant suicide note in which he denied ever doing anything that was not in the best interest of the country.

Mr. Ritchie says there were a total of 11 hearings into the Voice of America, much of them dealing with the editorial content of programming.

Senator McCarthy's closed-door hearings were followed by televised hearings that allowed millions of Americans to view his methods, sparking a public backlash that led to his Senate censure in December 1954. He died three years later of complications relating to alcoholism.