Italian investigators testified Friday in the murder trial of an American student and her former boyfriend, with one saying the American turned cartwheels in the police station after the killing.

A court in Perugia, in central Italy, heard testimony from detectives who inspected the apartment where 21-year-old Meredith Kercher, a Briton, was found stabbed to death on Nov. 2, 2007.

Kercher's roommate, University of Washington student Amanda Knox, and Knox's Italian former boyfriend, Raffaele Sollecito, are charged with murder and sexual violence. They were escorted into court Friday by police guards, and looked tense.

Domenico Giacinto Profazio, the former head of the Perugia flying squad, reconstructed the probe that led to the arrest of the two defendants as well as a third suspect, Ivory Coast national Rudy Hermann Guede. Guede was sentenced to 30 years in jail last year in a fast-track trial he had requested. All three deny wrongdoing.

Profazio said Knox and Sollecito had a "strange attitude" when they were brought to the police station for questioning following the discovery of Kercher's body. He said that on one occasion Knox sat on Sollecito's lap.

"I told them it was not appropriate," Profazio said.

He also recalled other officers reporting that Knox was doing cartwheels and splits in the police station.

Profazio also listed DNA evidence that prosecutors say points to Knox and Sollecito.

Prosecutors say Knox's DNA was found on the handle of a knife that might have been used in the slaying, and the victim's DNA was found on the blade. The knife was found at Sollecito's house.

They also say they found Sollecito's DNA on the victim's bra, although his defense team says the bra bore multiple DNA traces and maintain the evidence might have been inadvertently contaminated during the investigation.

Prosecutors allege that Kercher was killed during what began as a sex game, with Sollecito holding her by the shoulders from behind while Knox touched her with the point of a knife. They say Guede tried to sexually assault Kercher and then Knox fatally stabbed her in the throat.

On Saturday, forensic officers are also scheduled to take the stand.