Federal agents spied on the widow of Martin Luther King Jr. for several years after his assassination in 1968, according to newly released documents that reveal the FBI worried about her following in the footsteps of the slain civil rights icon.

Coretta Scott King might try to tie "the anti-Vietnam movement to the civil rights movement" according to some of the nearly 500 pages of intelligence files, which go on to show how the FBI trailed King at public appearances and kept close tabs on her travel.

The documents were obtained by Houston television station KHOU in a story published Thursday. Coretta Scott King died in January 2006. She was 78.

One memo shows that the FBI even read and reviewed King's 1969 book about her late husband. The entry made a point to say that her "selfless, magnanimous, decorous attitude is belied by ... (her) actual shrewd, calculating, businesslike activities."

The documents also focus on her relationship with Stanley Levison, who was a close adviser to Martin Luther King Jr. and a person the government long suspected was a communist.

There is also evidence that the Nixon administration and then-Secretary of State Henry Kissinger were kept informed of the FBI's surveillance.

Martin Luther King Jr.'s activities were long known to have been monitored by the federal government. News of intelligence gathering on famous Americans and war critics became so infamous that rules to curtail domestic spying were put in place in the 1970s.