Washington, United States: Forty-five years after inmates revolted at the US prison Attica, a historian has begun to unravel the tangled web of official lies about the ruthless suppression of the bloody uprising.

Heather Ann Thompson of the University of Michigan has gathered the results of 13 years of research into "Blood in the Water," a 720-page book on the 1971 incident in the upstate New York facility.

Still, she says the authorities refused her access to "hundreds and hundreds of boxes of materials."

"The evidence is clear that they don't want to do that because then the extent of the cover-up would be clear," she told AFP.

The uprising occurred at the end of a period of high-profile civil rights and racial justice battles in a country still struggling with race issues.

The summer of 1971 was coming to an end. Midway between Lake Erie and Lake Ontario in the western corner of New York state, the Attica prison held a majority of African American and Puerto Rican prisoners, monitored by guards who were virtually all white.

Conditions were appalling. Held in suffocatingly hot cells not renovated since the 1930s, prisoners received a mere half-gallon (two liters) of water a day, which they also had to use for their laundry and cleaning.

They were allowed only one shower a week and a single roll of toilet paper a month. The prison spent just 63 cents per prisoner per day to feed them.

- Treated like 'beasts' -

Prisoners were forced to work. "Black prisoners also endured the worst jobs," Thompson said.

There was other discrimination, whether religious -- Islam was banned -- or cultural, such as mail in languages other than English dumped in the trash.

It was in that context the revolt broke out on September 9, 1971. Around 1,300 prisoners seized control of the buildings, taking guards and other employees hostage.

"We are not beasts," one of the rebel prisoners declared amid intense negotiations that went into a fourth night.

"From the moment that the prisoners took over Attica, I believe that everybody in Washington, from the FBI to the army, the navy, the marines, the CIA, the attorney general's office and the office of the president were being informed of what was happening," Thompson said.

But on September 13, the governor of New York state, Nelson Rockefeller, sent in troops.

Advancing through clouds of tear gas, hundreds of police officers and national guards opened fire on the unarmed inmates.

Twenty-nine prisoners and nine hostages were killed and some hundred men were seriously wounded. A 10th hostage who was shot later died.

The explanation the authorities provided, and the media ran with, was that the prisoners had slit their hostages' throats.

"That was not true -- every hostage had been killed by law enforcement and by guns," Thompson said. "The government wanted to portray it as a black insurrection."

Combing through archives, the historian concluded that Rockefeller had purposely sacrificed the hostages' lives ordering the prison to be retaken by force.

"He made that decision even when everyone warned him that the hostages would die, that it was going to be a massacre -- and that's the word they used incidentally: massacre," she said.

- 'Black business', Mr. President -

"When it ended so terribly and so many prisoners were killed, all that (President) Richard Nixon wanted to know from the governor, Rockefeller, was 'was it a black business?'" Thompson said.

"And Rockefeller said: 'Yes, Mr President it was!' And of course once he (Nixon) felt that it was all black prisoners, he was fine with it, it did not bother him."

In the days and weeks that followed the uprising, guards and others exacted their revenge on prisoners. Many were tortured.

Nearly half a century later, the prisoners' protests and the false claims against them have had major -- paradoxically opposite -- repercussions, the historian said.

"In the immediate aftermath of Attica, there is a moment of great reforms" that made some prisons more humane, she said. "But it was very short-lived."

"Because the state officials lied about what happened and said that the prisoners had committed atrocities, it helped to turn this entire nation against civil rights and prisoners' rights," she said.

As a result, the United States began locking up more people than any country. 

"Attica became like the fuel for this engine that was punitive criminal policy."

In Sidney Lumet's 1975 film "Dog Day Afternoon," Al Pacino plans Sonny, a robber surrounded by police officers who takes bank employees hostage.

Looking to raise sympathy during the standoff, he shouts "Attica! Attica!"