The man convicted of raping and murdering a University of Vermont student will not face charges that he drugged and sexually assaulted other women before the 2006 attack.

The state has dropped the charges, which will not affect Brian Rooney's prison term.

Rooney was sentenced in September to life without parole for the aggravated murder of 21-year-old Michelle Gardner-Quinn of Arlington, Va., in October 2006.

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On Friday, prosecutors in Caledonia and Chittenden counties dismissed four charges against Rooney, including sexual assault on a person younger than 16; lewd and lascivious conduct with a child and repeated sexual assault.

At his sentencing, Rooney, a 38-year-old construction worker and father of three, fought back tears as he expressed condolences to the mother and father of Gardner-Quinn, but said he wasn't her killer.

"I am so sorry for what you are going through, but I am not the man responsible for this tragic event. And it saddens me to have to tell you that," he said.

Gardner-Quinn had just transferred to the school when she ran into Rooney on a downtown Burlington street Oct. 7, 2006. Her cell phone had gone dead and she asked to borrow his. They were seen on surveillance camera images walking past a jewelry store, but she vanished after that.

Six days later, her half-dressed body was found covered with leaves and stuffed into a rock crevice in Huntington Gorge.

The environmental studies major had been sexually assaulted, beaten and strangled after a night out with friends while her parents were in town for homecoming weekend.

Rooney was convicted largely because of DNA evidence from semen found inside her body in an autopsy.

Rooney's lawyer argued during his trial that the state's case lacked witnesses to the abduction and killing, and hinged on "two nanograms of sperm" handled by a forensic lab with a history of sloppy work.

Under Vermont law, the only available sentence for aggravated murder is life without parole.