A Skippack teen has been charged with stabbing his 17-year-old girlfriend to death in woods off the Skippack Trail on Saturday night.

Tristan Stahley, 16, was arraigned Sunday on charges including first-degree murder in the death of Julianne Siller, said Kevin Steele, Montgomery County first assistant district attorney.

According to court documents, Stahley and Siller, a high school senior who lived in Royersford, were at Stahley's family home on Rittenhouse Lane on Saturday when Stahley's mother overheard them arguing.

Soon after - and apparently reconciled - they left the house and drove in Siller's car to nearby Palmer Park in Skippack Township, where they argued again as they walked along the trail.

Stahley later told detectives he and Siller were arguing about his smashed cellphone and her "going out." He said he used an orange-handled knife and stabbed her in her throat and elsewhere, according to authorities.

They weren't sure yet about the number of wounds inflicted on Siller.

"So many times at this point that we do not have an exact count yet," Steele said.

After trying to hide Siller's body in the woods, Stahley returned home and told his mother he had broken up with Siller and killed her, authorities said.

"It's a tragic case," Steele said. "This young lady was scheduled to graduate soon from her high school and was planning on going on to college."

The Montgomery County Coroner's Office ruled Siller's death a homicide.

Stahley was being held Sunday at the Montgomery County Correctional Facility without bond.

Contact Carolyn Davis at 610-313-8109, cdavis@phillynews.com, or follow @carolyntweets on Twitter.