The first victim was a woman whose body was found with visible trauma in a home in Toronto last Tuesday. The next day, the police found a man dying of unspecified injuries in a Niagara Falls park, about 80 miles away. On Thursday, a man was fatally stabbed in a parking lot in Hamilton, a city some 45 miles from there.

That same day, the police in Canada arrested Sabrina Kauldhar, a 30-year-old Toronto woman who the authorities say had killed all three of those people in rapid succession. The motive for the killings was unclear, they said, noting that the last two victims had been targeted at random.

At a briefing with reporters on Friday, Chief Bill Fordy of the Niagara Regional Police Service described the attacks as having taken place on “a tight time frame.” He said that the authorities had undertaken an extensive search for the suspect, believing that the attacker might target others.

There was a risk she would commit further offenses, Chief Fordy said at the news conference. “I think by definition, she is a serial killer.”

The police connected Ms. Kauldhar to the two men’s deaths through a physical description, the authorities said in a news release. She was then linked to the victim in Toronto, a woman in her 60s.

On Friday, she was charged with murder in the three deaths. If convicted, she could face life sentences. The death penalty has been abolished in Canada.