PA teen Tristan Stahley charged with murder after stabbing 17-year-old girlfriend to death

A 16-year-old Pennsylvania boy was arrested on Saturday after police say he fatally stabbed his girlfriend as the two were arguing on a hiking trail in a park in a suburb of Philadelphia.

Tristan Brian Arthur Stahley has been charged with one count each of first-degree murder, third-degree murder, and criminal possession of a weapon after stabbing his girlfriend, 17-year-old Julianne Siller, to death. Siller was scheduled to graduate from high school in just three weeks.

Police in Montgomery County say the two teenagers got into an argument between 9 p.m. and 10:20 p.m. Saturday on the trail system in a park in Skippack Township.

'Killer': police say Tristan Stahley, 16 (right), fatally stabbed his 17-year-old girlfriend as the two argued on a hiking trail

According to authorities, Siller went to Stahley's home about 8:40 p.m. Saturday and the two began arguing.

The argument got so bad that Stahley's mother went to check on the couple, but was told by Stahley that it was 'none of her business,' and they both said they were fine.

About 15 minutes later, the couple told Stahley's mother they were going to the park and reportedly left the home holding hands.

RIP: Julianne Siller, 17, was found stabbed to death in the woods near a hiking trail

Once at the park, the two teenagers - who have been dating 'on-and-off' since January - got into another argument between 9 p.m. and 10:20 p.m., at which point Stahley produced an orange-handled knife and stabbed Siller repeatedly.

An autopsy report - first obtained by The Mercury - shows that Siller was stabbed and slashed multiple times, including injuries to her throat and neck.

"[Siller was stabbed] so many times at this point that we do not have an exact count yet," Montgomery County First Assistant District Attoey Kevin Steele told Philly.com.

After stabbing her, Stahley allegedly hid her body in the woods near the trail.

Stahley then ran home and told his mother he'd broken up with Siller and that he'd killed her. Family members then called police, and led authorities to Siller's body.

When police arrived at Stahley's house, the teen was involved in an altercation with his father, presumably over his admission that he'd stabbed Siller.

In the weeks leading up to the alleged murder, Stahley took to Twitter to level threats of violence against one of Siller's friends who called him a 'psycho.'

'say it to my face. I know you won't,' Stahley said in one of the threatening tweets.

'swear I won't stab you,' he continued in another. 'Just say it to my face if your not afraid.'

Stahley was arraigned this afteoon. He's been remanded to the Montgomery County Correctional Facility without bond.

'Crime scene': police say Tristan Stahley left his girlfriend's dead body in the woods near a hiking trail in a town park

Busted: Tristan Stahley has been charged with both first and third-degree murder