The main suspect in the murder of a University of Vermont student was being held Tuesday on unrelated sex charges while prosecutors expected new sexual assault charges to be filed against Brian L. Rooney.

"There is a pending investigation involving another women who complained of sexual assault involving Mr. Rooney," Assistant Attorney General Matthew Levine said Tuesday.

Levine said Rooney allegedly used a rag containing an ether-like substance to render the woman unconscious and then sexually assaulted her.

The Chittenden County state's attorney did not immediately return a phone call seeking information about the investigation.

Rooney, 36, had not been charged in the death of Michelle Gardner-Quinn, the 21-year-old UVM senior whose body was found by hikers near a gorge on Friday.

He was being held on $150,000 bail after pleading not guilty Monday to sexual assault and lewd or lascivious conduct with a child in the late 1990s.

The affidavit filed in Vermont District Court in St. Johnsbury says that Rooney several times used rags soaked in chemicals to knock his victims unconscious.

He is accused of assaulting a 15-year-old girl, who was the sister of a woman with whom he was living in East Concord in 1998.

"She awoke that night to him jumping on her in the bed and he forced a rag to her face," the affidavit said. "She quickly passed out ... When she awoke her legs were very weak, like Jello."

Rooney was charged years later because the alleged victim told police the details last week, Levine said.

Two women also filed relief from abuse petitions against Rooney accusing him of being abusive, including drugging them and having sex with them.

Burlington police have not given the cause of Gardner-Quinn's death.

In the affidavit, police said Rooney, of Richmond, denied any involvement in her disappearance.

On Tuesday, police asked the public to continue to search for items belonging to Gardner-Quinn, including a single black Converse low-top sneaker, a silver hoop earring, a Kyocera cell phone and a black Puma purse.

Gardner-Quinn was last seen with Rooney walking up Main Street in Burlington at about 2 a.m. on Oct. 7 after she had borrowed his cell phone after a night out with friends.