WASHINGTON (AP) - The Supreme Court on Wednesday seemed worried that allowing people to sue prosecutors who fabricate evidence to win convictions might chill other prosecutions - even if those prosecutors are doing their jobs correctly and honestly.

But justices also seemed frustrated at the thought that prosecutors could knowingly send an innocent person to prison - and then escape any repercussion by claiming that they were doing their job.

The case in front of the high court involves two former Pottawattamie County, Iowa, prosecutors, Attorney Dave Richter and his assistant Joseph Hrvol. They are being sued by Curtis W. McGhee Jr., and Terry Harrington, who were convicted of first-degree murder and sentenced to life in prison in 1978 for the death of retired police officer John Schweer. The men were released from prison after 25 years.

Evidence showed the prosecutors had failed to share evidence that pointed to another man, Charles Gates, as a possible suspect in Schweer's slaying.

They later on denied that Gates was even a suspect, even though witnesses placed him near the scene of the crime and his name appeared in several police reports. He also was administered and failed a polygraph test and the prosecutors themselves even consulted an astrologer about their suspicions of Gates.

McGhee and Harrington filed lawsuits against the former prosecutors, saying as prosecutors Richter and Hrvol had them arrested without probable cause, coerced and coached witnesses, fabricated evidence against them and concealed evidence that could have cleared them. They claimed authorities were eager to charge someone and that they were targeted because they are black.

Richter and Hrvol argued, however, that they were immune from lawsuits because they were acting within the scope of their job. Federal courts, however, said the immunity did not extend to their work before the trial began and rejected their motions to dismiss the lawsuits.

Ordinarily, prosecutors are immune from lawsuits based on their work at trial. This case tests whether that immunity stretches to the prosecutorial work that happens before the trial begins.

"If a prosecutor's absolute immunity in judicial proceedings means anything, it means that a prosecutor may not be sued because a trial has ended in a conviction," lawyer Stephen Sanders said.

But a couple of justices noted that under that theory, if a prosecutor fabricates evidence and gives it to another prosecutor to use at trial, they can be sued. But if a prosecutor fabricates evidence and then uses the evidence at a trial that they are working, they have immunity from lawsuits.

Justice John Paul Stevens called that idea "perverse."

"So the law is the more deeply you're involved in the wrong, the more likely you are to be immune? That's a strange proposition," Justice Anthony Kennedy said.

The court should not accept that proposition, said lawyer Paul D. Clement, who represented McGhee. "I can't think of a single reason why the only reason a prosecutor would get absolute immunity is, if they not only participated in the pretrial misconduct, but completed the scheme by committing further misconduct at trial," he said.

But several justices noted that if the court opens prosecutors up to lawsuits from those who are convicted for their actions before trial, it could make those prosecutors hesitate when it comes time to put bad guys on trial. "We're concerned about the chilling effect on prosecutors," Chief Justice John Roberts said.

For example, "this will discourage the prosecutors from becoming involved in the witness questioning process, at least not before the police are well on the way. And that is a very negative incentive, I would think," Justice Stephen Breyer said.

The point of the immunity is not to protect a bad apple, said Neal K. Katyal, a deputy solicitor general.

"It reflects a larger interest in protecting judicial information coming into the judicial process," he said. "And if prosecutors have to worry at trial that every act they undertake will somehow open up the door to liability, then they will flinch in the performance of their duties and not introduce that evidence."

The court will release its decision next year.

The case is Pottawattamie County v. McGhee, 08-1065.