GOLDEN, Colo. (AP) -- A Colorado teenager told a 911 dispatcher last fall that he kidnapped and killed a missing suburban Denver school girl and hid her remains in a crawl space at his mother's home, according to a recording played by a prosecutor in court Friday.

The recording was played at a preliminary hearing at which a judge decided there's enough evidence for Austin Sigg to stand trial in both the death of 10-year-old Jessica Ridgeway and an attack on a jogger at nearby Ketner Lake in May.

Westminster police Detective Michael Lynch testified at the hearing that Sigg first confessed to his mother, telling her that he kidnapped Jessica as she walked past his car, bound her arms and her legs, placed her in the back seat, drove around for a little bit, then took her to his house.

He had Jessica change clothes and tried to strangle her, first with zip ties and later with his hands, Lynch testified. He then took the girl's body to a bathtub where he dismembered her using a saw, he said.

Sigg, now 18, is charged with murder, kidnapping, sexual assault and robbery in Jessica's death.

Prosecutors have added three counts of sexual exploitation of a child because child pornography was allegedly found during the investigation.

He also faces an attempted kidnapping charge for the attack on the jogger. Attempted murder and attempted sexual assault charges have been dropped in that case.

Jessica's disappearance on her way to school on Oct. 5 set parents in the Denver area on edge for several weeks. Hundreds of officers canvassed the area, investigated leads and took DNA samples as parents waited with their children at bus stops and thought twice about letting them out of sight.

On Oct. 23, Sigg's mother called 911 to say her son wanted to turn himself in and had confessed to killing the girl. When the dispatcher asked what her son had said, Mindy Sigg replied, "That he did it, and he gave me details, and her remains are in my house."

She can be heard crying and asking if her son will talk to the dispatcher, who asks him general questions.

"I don't exactly get why you're asking me these questions. I murdered Jessica Ridgeway. I have proof that I did it," Austin Sigg said. "You have to send a squad car down here, and I'll answer any questions you want to ask me."

He also said the remains were in a crawl space.

When asked about his criminal record, he told the dispatcher: "The only other thing that I have done was the Ketner Lake incident where the woman got attacked. That was me."

Mindy Sigg told investigators that her son appeared sick the day he confessed and said he opened the conversation by saying he was a "monster," Lynch testified.

The teen had been on investigators' radar before his mother turned him in. A neighbor called a tip line suggesting they check him out because he seemed preoccupied with death, Westminster police Detective Luis Lopez said.

Two FBI agents responded and took a DNA sample from Sigg on Oct. 19, four days before his mother called 911.

Lopez said Sigg's DNA -- the kind left behind by touching something -- was found on Jessica's clothing, but no semen was found.

Sigg told investigators that he didn't rape Jessica, Lynch said.

"It was a comment he had made right off the bat, 'I didn't rape her. I didn't torture her."'

Some of Jessica's remains were found in garbage bags in an open space park five days after she went missing. Friday was the first time investigators revealed that the bags contained her torso. Lopez testified that she died of asphyxiation.

The judge originally ordered Friday's hearing to be closed to the public but the Colorado Supreme Court sided with media organizations who argued that he failed to show that holding the hearing in public would jeopardize Sigg's right to a fair trial.

Arraignment is set for March 12.