Special prosecutors investigating allegations that police tortured nearly 150 black suspects in the 1970s and '80s said Wednesday they found evidence of abuse, but any crimes are now too old to prosecute.

In three of the cases, the prosecutors said the evidence was strong enough to have warranted indictments and convictions.

"It is our judgment that the evidence in those cases would be sufficient to establish guilt beyond a reasonable doubt," Robert D. Boyle and Edward J. Egan wrote.

The four-year investigation focused on allegations that 148 black men were tortured in Chicago police interrogation rooms in the 1970s and '80s. The men claimed detectives under the command of Lt. Jon Burge beat them, used electric shocks, played mock Russian roulette and started to smother at least one to elicit confessions.

No one has ever been charged, but Burge was fired after a police board found he had abused a suspect in custody. His attorney has said Burge never tortured anyone.

The report released Wednesday also faulted procedures followed by the Cook County State's Attorney's office and the police department at the time of the alleged abuse, saying they were "inadequate in some respects" but had since improved.

Mayor Richard M. Daley was the state's attorney during part of the period investigated.

Daley's office did not immediately return a call for comment Wednesday. A police spokeswoman also did not immediately return call seeking comment.

Boyle and Egan said they found three cases with enough evidence to seek indictments, including one involving the man whose abuse allegations led to Burge's firing. The man, who was convicted of killing two police officers in 1982, claimed Burge and two detectives beat and tortured him with electric shocks.

"Regrettably, we have concluded that the statute of limitations would bar any prosecution of any offenses our investigation has disclosed," the prosecutors said. The statute of limitations on the allegations is three years.

They also said they believe there was abuse in other cases but that the evidence wasn't as strong.

Several people who claimed to have been abused or tortured by Chicago detectives have filed civil lawsuits against the city and police department, and the report could bolster their legal claims.

There had also been a legal battle over the release of the report. The Illinois Supreme Court eventually denied a request from a former prosecutor, listed in court documents only as "John Doe," to block portions of the report from being released.

In May, a United Nations anti-torture panel said the Chicago investigation needs to go farther than it has. The panel said the United States should ensure that law enforcement officials who mistreat suspects are punished.