Matthew Oropeza was following his routine on the night of Jan. 5 when he drove his two dogs to Gold Star Park in South Philadelphia and let them run unleashed.

But that Saturday night, Drew Justice and his fiancee, Kristi Buchholz, were walking their black shih tzu shortly after 9 p.m. on the sidewalk outside the park when Justice yelled out to Oropeza to put his dogs on leashes, Buchholz told police.

“What did you say?” witnesses said Oropeza responded. “Say it to my face.”

That comeback, detailed in a police affidavit obtained by the Inquirer and Daily News containing statements from witnesses and Oropeza, signaled what came next: an encounter that resulted in the death of Justice. Police last week charged Oropeza with involuntary manslaughter, simple assault, reckless endangerment, and making terroristic threats.

According to the affidavit, Justice walked into the park and Oropeza approached him. Oropeza told police that he didn’t know Justice but didn’t appreciate his comment. Justice, the document says, raised his hands, and Oropeza beat him to the punch with a quick left jab. Oropeza said he watched him fall back and hit his head on the ground.

Oropeza, witnesses told police, then gathered up his dogs and left the park through the Wharton Street entrance.

“You have to call an ambulance,” one witness told him. Oropeza, the witness said, waved her off, slid into a gray 2016 Honda Civic, and drove away.

Police responding to a report of “a person screaming” found Justice with another person on top of him pumping his chest in an attempt to perform CPR. A pool of blood was spreading around his head. He was taken to Thomas Jefferson University Hospital, where he was pronounced dead at 9:51 p.m.

The Philadelphia Medical Examiner’s Office ruled that Justice, a 38-year-old data management programmer who lived across the street from the park, died from a “blunt impact trauma injury to the head." He was buried in a private ceremony last week.

Oropeza, 24, had moved into an apartment on the 1600 block of South 16th Street in July with his girlfriend and their 2-month-old son. In the months since, he would regularly walk in the park, bounded by Wharton, Marshall, Manton, and Sheridan Streets between Sixth and Seventh, with their dogs: Coco, a fluffy, white shih tzu, and Bentley, a brown German shepherd/border collie mix.

Court records show that Oropeza, who lived in Delaware County between 2013 and 2018, had been arrested there twice for fighting — in Brookhaven in 2013 and in Ridley Township in 2016.

In his statement, Oropeza told police the fatal confrontation with Justice was not his first dispute in Gold Star Park over his habit of walking his dogs without leashes. He said he had a verbal run-in with another man about the same issue Jan. 1.

Justice was a 1999 graduate of George School, a Quaker high school in Newtown, Bucks County. He earned a bachelor’s degree in computer science from Philadelphia University in 2003.

Buchholz, his fiancee, is a lawyer and a board member of the Passyunk Square Civic Association. The association’s website says she is active in organizing events and fundraising for Gold Star Park. The couple were to be married in April, according to their online wedding registry page.

Oropeza, who is free on bail, is scheduled to have a preliminary hearing Jan. 30. In Pennsylvania, involuntary manslaughter is a first-degree misdemeanor punishable by up to five years in prison.