CONCORD, N.H. — Prosecutors are asking a judge to sentence a graduate of an elite New Hampshire prep school to 3 ½ to 7 years in prison for using a computer to lure a younger classmate to a nearly deserted school building where he sexually assaulted her. Prosecutors said Thursday they also want 20-year-old Owen Labrie, of Tunbridge, Vermont, to complete a sex offender program. Labrie was convicted in August of misdemeanor sexual assault plus the felony count of using the computer to lure the girl to the encounter.