ADAMS TWP — A 13-year-year-old Middlesex Township girl was killed Thursday afternoon when the pickup driven by her sister slammed into two trees along Denny Road, authorities said.

Randi Stritzinger, an eighth grader at Mars Middle School, died "instantaneously," said Butler County Deputy Coroner Larry Barr, when the passenger side of the Dodge Ram pickup crashed into the second large oak tree.

Randi and her sister, Nikki, 17, a student at Mars High School, were on their way home from school about 2:45 p.m. when the crash occurred — a mile or so from the school and about 3 miles from the girls' house.

"We believe at this point speed was a factor," said Adams Township police Sgt. Shawn Anglum.

Barr pronounced Randi dead at the scene at 4 p.m. An autopsy Thursday night determined the girl died of massive injuries to her chest and body.

Nikki was not seriously injured, authorities said. However, she was taken by Quality Ambulance to Allegheny General Hospital in Pittsburgh, investigators said, and given a precautionary examination.

Police continue to investigate the crash on Denny Road — a secondary road well-traveled by Mars students on their way to and from school.

The two-lane road allows students to connect to Route 8 and avoid the traffic congestion of Route 228.