Fatal stabbing on Montour Trail leads to guilty but mentally ill plea

The person who killed a Pennsylvania State Police Liquor Control Enforcement agent last year on the Montour Trail pleaded guilty but mentally ill on Monday to third-degree murder.

Antonia Quesen, 26, will be sentenced Nov. 18 by Allegheny County Common Pleas Judge Edward J. Borkowski.

In Pennsylvania, a person who pleads guilty but mentally ill is still incarcerated in state prison. However, the law requires they be placed in a facility that meets their mental health needs.

Quesen pleaded guilty to killing Benjamin Brallier, 44, of Coraopolis.

According to investigators, Brallier was off-duty and running on the Montour Trail in Moon the afternoon of Oct. 21, 2024, when he was attacked.

Quesen had been living in the woods near the trail, according to Assistant District Attorney Chase Stelzer.

The prosecutor told the court that Brallier, who had de-escalation training, had a lengthy interaction with Quesen before being stabbed multiple times in the upper back, torso and hand.

Moon police dispatched officers for a medical call and found bystanders attempting to help Brallier, who wasn’t breathing.

He died at Heritage Valley Sewickley hospital just before 4 p.m.

Investigators found signs of struggle, including a trail of blood leading to a bicycle, according to the criminal complaint.

State troopers found Quesen just after 10 p.m. about three-tenths of a mile away with blood on her clothes and hands, as well as wounds on her hands caused by “sharp-edge trauma from slippage,” Stelzer said.

Quesen’s attorneys told the court on Monday that she previously had been diagnosed with schizoaffective disorder and post-traumatic stress disorder.

Quesen was treated at Torrance State Hospital for several months, but Borkowski in July said she was competent to stand trial.

As part of Monday’s proceedings, Quesen also pleaded guilty but mentally ill to a 2023 robbery at Point State Park.

According to Stelzer, a man was walking through the park with his son when Quesen attacked them unprovoked on June 24, 2023.

There was a struggle over the victim’s cellphone, Stelzer said, which resulted in Quesen ripping off the man’s Fitbit watch and throwing it in the river.

The victim suffered a sprained knee. Quesen fled by jumping in the river.

After she was arrested, Quesen was granted bond with a recommendation that she follow up with mental health treatment.

However, after that, she failed to appear for three preliminary hearings, and bench warrants were issued.