ILLINOIS ? A teenager accused of helping his ex-girlfriend kill and dismember a 16-year-old classmate pleaded guilty to murder Thursday in a deal with prosecutors that could shorten his sentence by decades.

Cory Gregory, 18, had led authorities to the girl’s remains, which had been chopped up, burned and dumped in two counties, Rock Island County State’s Atty. Jeff Terronez said.

He faces 20 to 40 years in prison at his sentencing July 10, plus two to five years for an earlier plea to concealing a homicide.

Under the deal, approved less than a week before his murder trial was to begin, Gregory will not face additional dismemberment and murder charges that could have added 50 years to his sentence.

Prosecutors say Gregory and Sarah Kolb, 18, killed Reynolds in Kolb’s car over their school lunch hour at a fast-food restaurant on Jan. 21, 2005, then took the body to Kolb’s grandparents’ farm and burned it.