SASKATOON -- A doctor who once worked at a Saskatoon hospital has been charged with murder in Ontario following an investigation into suspicious deaths.

Ontario Provincial Police were called to the Hawkesbury and District General Hospital Thursday evening.

Dr. Brian Nadler, 35, was arrested at the hospital and has been charged with first-degree murder. He appeared in court in L'Orignal, Ont., near Hawkesbury, on Friday.

"Dr. Nadler maintains his innocence," his lawyer Alan Brass told CTV News Ottawa. Brass said the charges against Nadler will be rigorously defended.

Police say they are investigating suspicious deaths.

“At this point in time, the number of deaths is part of the ongoing investigation,” OPP spokesman Bill Dickson said.

"We gathered evidence and witness testimony that led us to the grounds to lay that one first-degree murder charge, but the investigation is definitely ongoing. We are still in the early stages."

Nadler was found guilty in 2018 of unprofessional conduct while practicing at St. Paul's Hospital in Saskatoon.

After a verbal altercation with another physician, he referred to that physician as a "b---h" in discussion with a senior resident, according to the college.

He also told the resident that during the altercation with that doctor, he "felt like slapping her."

Nadler also added a reference to a medical record without noting the date and time.

The matter was resolved when Nadler agreed to take courses in "professional ethics and medical record-keeping" and to write a letter of apology, the college's website says.

He became a member of the Ontario College of Physicians and Surgeons in February 2020.

Nadler remains in custody and is next due in court on April 6.

Hawkesbury is about 110 kilometres east of Ottawa, near the border with Quebec.

With files from CTV News Ottawa