A man who identified himself as a police officer barged into a man's Squirrel Hill apartment on Sunday evening, attacked him and then followed him to a nearby pizzeria where employees were forced to intervene, according to a criminal complaint.

Police said Matthew Morrow, 34, of Swisshelm Park, pounded on the door of the Murray Avenue apartment belonging to David Russell. When Mr. Russell asked who it was, Mr. Morrow told him it was the police.

After Mr. Russell opened the door, he said he was struck in the face with an unknown hard object. Police said Mr. Russell  had a “large and deep” laceration near his left eye, cuts to left side of his face, and was "bleeding profusely.”

Police said Mr. Russell fled his apartment and went to nearby Mineo's Pizza House, where he was again confronted by Mr. Morrow.

Employees there heard an argument and stepped in when they said Mr. Morrow picked up a chair and held it over his head "in an aggressive manner." In the complaint, police officers said surveillance footage matched the description provided by Mineo's employees.

Police did not say what prompted the attack or why Mr. Russell was targeted, but said the incident was corroborated by neighbors, who said they heard someone yell "police" outside the apartment. One neighbor reported hearing a man yell, " ‘Show me your hands. Get on the ground,’ " the complaint said.

During the investigation, police said they were able to follow a blood trail from Mr. Russell's apartment to the pizzeria. The attack began around 8 p.m.

Mr. Russell was transported to UPMC Mercy, where he was in stable condition.

Police have charged Mr. Morrow with aggravated assault, simple assault, burglary, harassment and impersonating a public servant.

A preliminary hearing is scheduled for May 8.

First Published: May 1, 2018, 8:47 p.m.