MADISON, Wis. (AP) -- Court records show a convicted sex offender has been jailed on a probation hold and is considered a material witness in the death of a University of Wisconsin-Madison student from Marshfield.

A Madison television station disclosed this evening that documents seeking to revoke David Kahl's probation quote him as telling police he broke into a home near 21-year-old Brittany Sue Zimmermann's apartment on the day she was killed, and that he knew two homeless men who were running scams and breaking into houses.

The station says he also helped police develop a sketch of one of the men.

The records say he's being treated by police as a material witness, not a suspect.

Zimmermann's fiance found her body April second in their first-floor, off-campus apartment several blocks from the state Capitol.

Investigators have said Zimmermann's door was forced open.

A Dane County Jail spokeswoman confirms the 42-year-old Kahl remains in custody Monday night.

Computerized state court records show his record includes a second-degree sexual assault conviction in a 1993 case where he pleaded no contest and was sentenced to a year in prison.