In some cases, prisoners who refused to stop fighting were shot dead. In a ritual that became known as "gladiator days", known enemies at Corcoran State Prison were released from their cells and paired off like fighting cocks in empty prison yards.
The fights became such events that officers of other units were called as spectators. The chief witnesses to the brutality at Corcoran, built in 1988 as a hi-tech security jail and whose 5,500 inmates include the cult leader and murderer Charles Manson and Robert Kennedy's assassin, Sirhan Sirhan, were a group of prison officers who went to the FBI, the newspaper said. Agents of the FBI have been gathering evidence for about a year and a grand jury is investigating the shootings to see if a prosecution can be brought.
The worst abuses were said to occur under the tenure of warden George Smith, who retired last July and was dubbed "Mushroom George" because "mushrooms like to be kept in the dark", one guard said. Mr Smith kept a picture of John Wayne in his office to project a tough image and turned a blind eye to his subordinates' tactics. Over a period of eight years seven inmates were shot dead at Corcoran, five in the 18 months after Mr Smith took over. More than 50 have been wounded, more than in any other prison in the United States. Gunfire rang out almost every day, and shootings were covered up, officers say.
The disclosures from the prison, built in California's San Joaquin Valley, come against a drumbeat of demands for tougher treatment of prisoners in US jails. Most recently Bob Dole, in his speech accepting the Republican Party's nomination, promised to make life "hell" for violent criminals.
Guards and inmates described macabre scenes in which prison officers gathered in control booths overlooking cramped exercise yards in advance of fights, which were sometimes delayed so that female guards and even prison secretaries could be present. The officers were armed with gas guns that fired wooden blocks, and rifles.
The excuse for pairing off prisoners, often members of rival black and Latino gangs which exercise powerful control over the inmates, was an official policy of "integration". It mandated bringing long-time rivals together at close quarters in the hope that they would learn to live and let live. The policy was widely derided as a loser that forced inmates into fights and left officers with split-second decisions about life or death, and it has now been rescinded.
But at Corcoran's Security Housing Unit (SHU), reserved for 1,800 problem inmates sent from other prisons, it was allegedly perverted into a system of staged brawls. Dimas de Leon, an SHU inmate from 1988 to 1990, claimed to have been involved in 11 staged fights in which his boxing skills made him a favourite.
"I was made aware by officers that there was money riding on me to win," he said in an affidavit. "I was even thanked by officers for making them a bit richer." But it was the killing of Preston Tate, a 25-year-old gang member from South Central Los Angeles, that persuaded several officers to become whistle-blowers. He died in April 1994 after officers opened fire in a section of the SHU known as the "shooting gallery".
A videotape, which is now the basis of a law suit filed by his family, showed Tate, who was black, being charged by two Latino gang members and eventually being shot in the head as guards opened fire to break up the fight. An official report cleared the officers of wrongdoing. But Steve Rigg, a Corcoran lieutenant for six years and one of those co-operating with the FBI in a civil-rights investigation into the incident, became convinced the fight was rigged. Tate had recently been moved into a cell adjacent to his assailants, and in another tell-tale sign, a number of supervisors had gathered in the control booth. It was the second watch in the same building that is suspected of staging a series of "cockfights".
In eight months in 1994, 85 fights broke out in the period from 6am to 2pm, by contrast with just eight fights in the third watch, overseen by Mr Rigg. "They wanted to create fights," he said. "I think they liked shooting at some of the troublemakers. They wanted to get their little ounce of revenge."
In other incidents at Corcoran, a group of officers dubbed "the Sharks" organised reception parties for busloads of arriving prisoners who were pummelled and kicked. After an internal investigation, three senior officers were dismissed and five other lieutenants and sergeants were demoted or suspended. While a grand jury is investigating other incidents, the failings of the integration policy may help to protect officers from any criminal investigation, prosecutors say.