Tess Richey was strangled to death around last time she was seen alive near the Church Street stairwell where her body was found, a forensic pathologist testified Wednesday.

Dr. Kona Williams said her opinion was based on marks on Richey’s neck and internal bleeding consistent with sustained “neck compression” that would have caused her to first pass out and then, within minutes, die.

Williams testified she could not say exactly how the pressure was applied — whether by a piece of clothing, a chokehold or, as prosecutors have suggested, a forearm pinning Richey against a hard surface.

The Crown alleges Kalen Schlatter, then 21, sexually assaulted and murdered 22-year-old Tess Richey after she refused to have sex with him in a stairwell outside a home under construction on Church St. in the early hours of Nov. 25, 2017.

Schlatter has pleaded not guilty to first-degree murder.

According to an autopsy, Richey had an abrasion on one side of her forehead, as well as bruising on her forearms, wrists, the inner part of her knees, and the back of one of her hands.

“Potentially there may have been an element of a struggle,” Williams said. “But again the injuries are not 100 per cent specific.” The injuries to Richey’s lower legs could have come from falling, but there are no other injuries that would suggest she’d fallen repeatedly, Williams said. The injuries to her forearms, wrists and hands suggested she could have been restrained or held down, Williams said.

Williams said it was difficult to know an exact time of death. Richey’s body was found on the afternoon of Nov. 29, 2017, four days after she was last seen alive. However, Williams said, the state of her body was consistent with a time of death around the last time Richey was seen alive, at around 4:15 a.m. on Nov. 25, 2017.

The Crown has said surveillance video shows Richey and Schlatter walking into an alley on Church St. and towards the stairwell where her body was found at about 4:14 a.m., and then, 45 minutes later, Schlatter leaving alone.

Under cross-examination, Williams agreed Richey could have died between 5 a.m. and 6 a.m. or any other time afterwards on Nov. 25, 2017.

The trial continues.