Juan Rivera began acting bizarrely shortly after he first admitted killing Holly Staker, a detective testified Thursday.

Rivera, 36, is on trial for the third time for the Aug. 17, 1992 rape and murder of the 11-year-old Waukegan baby sitter. He has twice been found guilty and sentenced to life in prison, but new trials were ordered after each conviction.

Around 3 a.m. on Oct. 30, 1992, Rivera had just finished telling two detectives from the Lake County Major Crimes Task Force how he had killed the girl, and those detectives went to prepare a typewritten account of what Rivera had said.

Detective James Held testified Thursday he was asked to keep an eye on Rivera, who was in an interview room at the Lake County sheriff's office, while the other officers were away.

Held said he observed Rivera through the one-way glass from an interview room next to the one Rivera was in. Rivera walked up to the glass on his side of the wall, Held said, and cupped his hands on the mirror and tried to look through it.

Held said Rivera then turned away from the mirror, stood in a corner of the room and began "tapping" his head against the wall.

"I watched him to this for about 20 or 30 seconds," Held said. "Then I walked over to the room he was in and asked him to stop doing that."

Rivera did not respond, Held said, but kept tapping his head against the wall in a light, rhythmic manner.

Held said he then went to get another officer and when they returned to the room, Rivera was crouched in the corner and was still tapping his head against the wall.

Other officers converged on the room, Held said, and together they laid Rivera down on the floor and handcuffed him.

"He had begun hyperventilating at the time and was still not responding to any of our verbal instructions," Held said. "We wanted to get his hands secure to prevent him from harming himself."

Rivera seemed to calm down after a few minutes, Held said, but officials decided to return him to the jail.

Rivera was brought to his feet, Held said, taken to the jail and placed in a padded observation cell near the booking desk.

Defense attorneys have characterized the episode as a "psychotic event," and claim it is proof Rivera was not competent to confess to the crime.

During his cross-examination of Held, defense attorney Thomas Sullivan attempted to pose a series of questions concerning police questioning of Rivera on Oct. 29 and Oct. 30 that led to his confession.

Sullivan asked Held if he was aware Rivera had a low IQ, was emotionally unstable and if Held was aware that some experts maintain questioning a suspect for more than four hours can prompt a false confession.

Circuit Judge Christopher Starck sustained all of Assistant State's Attorney Eric Kalata's objections to those questions and Held did not answer them.