CHICAGO (AP) _ An appeals court has ordered a new trial for a stable owner convicted in 1995 of the deaths of three boys whose bodies were found in a forest preserve four decades earlier.

In its 2-1 ruling, the Illinois Appellate Court on Thursday reversed the murder conviction of Kenneth Hansen, who is serving a 200-year prison sentence for the 1955 slayings.

Justice Thomas Hoffman wrote that the trial court erred in allowing testimony ``regarding the defendant's practice of picking up young male hitchhikers and sexually assaulting them.''

``Improper evidence of a defendant's sexual conduct with children is so prejudicial as to normally require reversal,'' the appeals court said.

Bob Benjamin, a spokesman for Cook County State's Attorney Richard Devine, said prosecutors would ask the appeals court to reconsider or take the case to the Illinois Supreme Court. He said prosecutors would fight any attempt by Hansen to be released on bond.

``We disagree with this decision,'' Benjamin said.

Robert Petersen, 14; John Schuessler, 13, and his brother, Anton Schuessler, 11, are believed to have met their killer while hitchhiking after leaving a bowling alley.

The case baffled police until Hansen was charged and tried in 1995.

At the trial, witnesses testified that Hansen had spoken on several occasions over the years of killing the three boys. Hansen was quoted by one witness as saying that one of the older boys came into the barn while he was having sex with the youngest, and threatened to tell. He strangled that boy and then killed the two others to silence them, according to the account.