BUTLER TWP — State police investigators have not ruled out the possibility that the fatal weekend shooting by an off-duty trooper of his neighbor was an incident of “suicide by cop.”

Police suspect that moments before 25-year-old Kristopher A. “Kit” Barkus left his family’s home on September Drive Friday night, he threatened to take his own life.

He already was on medication for depression, investigators said.

He walked just several homes down the block to Trooper Brian Knirnschild’s house. He appeared at the front door just after 8:30 p.m.

Barkus’ family called 911 to report the unfolding crisis and went looking for him.

Knirnschild told first-responding police officers that he noticed his young daughter was standing at the door inside the house, pointing outside.

The trooper went to the door and “saw Barkus standing outside brandishing a handgun,” according to court documents that police filed in the investigation.

A trooper for less than two years, Knirnschild began “to issue commands for Barkus to drop his weapon.”

Barkus’ gun was silver with black grips. But, investigators acknowledged, it was not a real gun. It was an Airsoft pistol. A replica Beretta 9 mm model — something Knirnschild didn’t know.

The trooper fired his gun at least three times, hitting Barkus in the stomach at least twice, police said.

Knirnschild’s wife was home and called 911, telling the dispatcher that her husband shot a man on their property. The call came in at 8:40 p.m.

Just before or about the time of the shooting, police believe, Barkus’ older brother, Bobby, spotted his sibling and pulled into Knirnschild’s driveway, but apparently too late.

Catty-corner from Knirnschild’s house, neighbor Barbara Greco was at home when she heard what she immediately knew was gunfire.

“There were several shots,” she recounted. “I don’t know how many because it happened so fast.”

At first, she thought they were coming from below her house. She eased her way outside and noticed the shooting was closer to her home than she thought.

Down the street and washing his car, another neighbor heard the shots. The 27-year-old man, who did not want to give his name, initially gave it little thought.

“I thought someone was shooting at an animal or just firing a gun,” he said. “That happens here.”

Nevertheless, he slow-trotted up the street to check out the commotion. Suddenly, he said, a silver Volvo sped past him.

“It was going pretty fast,” the man said, “probably 45 to 50 (mph).”

It was getting dark out by then and he couldn’t make out who was inside. But he saw two people and he knew that car belonged to Bobby Barkus.

Authorities believe the older brother drove Kristopher Barkus to Butler Memorial Hospital, where a medical helicopter later flew him to a Pittsburgh hospital.

But at 10:31 p.m., he was pronounced dead at Allegheny General Hospital.

An autopsy completed Saturday afternoon determined Barkus died of “a gunshot wound to the trunk,” according to the Allegheny County Medical Examiner’s Office. The manner of death is listed as homicide.

Forensic investigators said they could not provide any additional information, such as who many times Barkus had been shot or the caliber of the bullet that killed him.

Police also are being tight-lipped.

“There are still questions that we’re trying to answer,” Cpl. Dan Herr said Saturday, “and our investigation continues.”

While Butler Township police got the initial call, state police took over the case in part because it involved one of their own, Herr said.

Along with the probe by the state police major case unit, the department’s internal affairs division will conduct its own investigation, as it does all shootings involving officers.

Additionally, the Butler County District Attorney’s Office has been notified.

“We’ll review the police report once they’ve completed the investigation,” said District Attorney Richard Goldinger, “and then determine if criminal charges are warranted or not.”

Township Patrolman Tom Palla was the first officer on scene. He spoke with Knirnschild and took down the trooper’s immediate account of what happened.

Soon after, township Detective Dave Fish got to the house and noticed two guns — Knirnschild’s .380-caliber pistol and Barkus’ Airsoft gun.

Other evidence was apparent, too, namely three shell casings, a live .380-caliber round and a black back pack.

Police said the back pack belonged to Kristopher Barkus. It contained some of his prescription medication and drug paraphernalia.

Herr said state police are investigating the case by the book.

“We’re handling it no differently than any other shooting,” Herr said.

He said police immediately secured the scene, spoke to all parties involved and canvassed the neighborhood.

Investigators learned from Bobby’s fiance, who lives at the Barkus’ family home, that Kristopher had “left the residence angered about something,” police documents said.

She told police that she knew that Barkus was taking medication for depression.

Herr confirmed that Barkus had numerous prescriptions but he could not say what they were.

The fiance also remembered that Barkus had left the home with a black backpack. And before he left, he made an ominous comment.

He said “that he was going to jump off a bridge,” documents said.

Investigators five hours after the shooting obtained two search warrants for the Knirnschild and Barkus homes. District Judge Wayne Seibel signed the warrants at 1:50 a.m. Saturday.

At Knirnschild’s home, police were allowed to seize all handguns owned by the trooper, the gun that Barkus allegedly brought there, and any shell casings, expended rounds, clothing, blood and any other trace evidence.

At Barkus’ home, troopers sought all prescriptions medications, any “suicidal notes” that Barkus had written and any of his computers, cell phones or other devices with Internet access, the search warrant application said.

Investigators believe the preliminary findings suggest that Barkus may have intended to be killed, and one theory they were looking at was “suicide by cop.”

That term describes fatal police shootings in which a suicidal person deliberately behaves in a way that leads to officers opening fire.

Herr said Barkus knew that Knirnschild was a trooper.

Police also acknowledged that in the weeks leading up to the shooting, Barkus had showed up uninvited at Knirnschild’s house. The nature of that earlier visit wasn’t immediately clear.

Court records showed that township police cited Barkus for harassment after he allegedly shoved a family member May 17. He had pleaded not guilty to the citation, according to records at District Judge Kevin O’Donnell’s office.

Barkus also had two prior convictions for driving under the influence of drugs.

Attempts by the Butler Eagle to reach the Barkus family for comment were unsuccessful.

Neighbors said the Barkus family has lived on the street for many years and that the Knirnschilds are relatively new to the neighborhood.

The real-estate listing website Zillow.com showed that the house where the Knirnschilds live was last sold in August 2013.

A 2004 graduate of Seneca Valley High School, Knirnschild graduated from the state police academy in December 2012, the department said.

In 2011, while in the Army Reserve, he returned following deployment to Iraq as part of Operation Iraqi Freedom and Operation New Dawn.

Herr said that Knirnschild, in wake of the shooting, has been placed on paid administrative leave, in keeping with police policy.

Meanwhile two neighbors who grew up with Barkus recalled that he was a gifted musician and excelled in sports, including swimming, baseball and football.

He was a 2007 graduate of Butler High School and later attended the Berklee School of Music in Boston.

Funeral arrangements are being handled by the McDonald-Aeberli Funeral Home, Mars.