VANCOUVER -- Vancouver police say the victim of the city's ninth homicide was engaged in a fistfight when he was fatally stabbed.

Thomus Donaghy, 41, was killed outside St. Paul's Hospital Monday night while on break from a shift at the nearby Overdose Prevention Site.

In an appeal for witnesses Friday, Vancouver Police Department spokesperson Sgt. Aaron Roed said Donaghy had been in a fight that became deadly.

"He was involved in a fistfight with an unidentified man," Roed said. "Initially this may have looked like a fistfight in the area of Comox and Thurlow (streets) and people may have dismissed it as that, not knowing the severity of the incident."

Police have not publicly identified a suspect yet.

Following Donaghy's death, fellow volunteers and workers at the OPS said it's frightening to see that level of violence near their workplace.

"When a person goes on his break and all of a sudden, they wind up dead, that's a pretty scary thing," said Rodney, a volunteer who only gave his first name.

At the OPS, peer volunteers watch over users to make sure they don't have a fatal reaction, often administering drugs like naloxone to counteract the effects of the opioid. Users have to supply their own drugs, however.

The co-executive director of RainCity Housing, the organization that manages OPS, told CTV News she'd heard Donaghy was a strong advocate for harm reduction and overdose prevention.

"He did a lot of work with peer-based organizations and other organizations to help support and keep safe people that use drugs," Catharine Hume said Friday.

"My understanding from a number of people that I have spoken to is that he had a profound impact in terms of working to be a real leader in overdose prevention work across the city."

Calling his death a tragic event, she said the organization is taking it seriously and working closely with WorkSafeBC, Providence Health Care and Vancouver Coastal Health.

"We'll also be doing a lot of internal review and learning as much as we can in order to create as much safety as possible at the OPS moving forward," Hume said.

Anyone with information or dash-cam footage is asked to contact VPD at 604-717-2500. Tips can also be left anonymously with Crime Stoppers.

With files from CTV News Vancouver's Jon Woodward, Sheila Scott and Cameron Mitchell