Washington County Assistant State's Attorney Duane Gigeous said only Jeffrey Gordon Snyder, now 18, of Smithsburg, remains to be prosecuted.
Two other teenagers, tried as juveniles, both pleaded guilty earlier to fourth-degree sex offenses. One of the youths was placed on probation while the other was sent to the Charles H. Hickey Impact Center in Baltimore for 60 days.
Gigeous told Moylan that the victim recalled Langenstein telling the other boys that night to leave her alone.
Langenstein admitted he later helped hold her arm while others tied her to the bed.
"I'm extremely upset over what happened to the victim," Langenstein said. "I can't say I did enough to stop it, but I did try."
Langenstein said he realizes he needs drug and alcohol treatment.
According to police reports, the victim, who was 16 in May 1995, was hired tobaby-sit for a child at the home of one of the boys. She arrived in mid-afternoon for a barbecue at which the four boys were present, prosecutors said.
After midnight, the victim was forced into a bedroom and tied to a bed, police reports said.
The mother of one of the boys returned home and walked in on the incident, police reports said.
"The victim was where she was supposed to be, doing what she was supposed to be doing," Moylan said, referring to the fact that she was baby-sitting a young child that night.
He ordered Langenstein to complete the Jail Substance Abuse Program and after-care when he is released. During his three years of supervised probation, Langenstein was ordered to abstain from all drugs and alcohol, pay restitution of $422 for counseling and get his high school equivalency diploma.