When Toronto police confronted a knife-carrying Sammy Yatim on an empty streetcar early Saturday, bystanders grabbed their cellphones, turned on the video function and hit record.
What they captured – images of police ordering Mr. Yatim to "drop the knife"; Constable James Forcillo appearing to fire his gun at him nine times; and then another officer using a taser on him after he was shot – has riveted the city.
It has also riveted police, whose quest at the scene that night to obtain copies of the videos left some bystanders wondering whether they were under any legal obligation to comply.
"I had no idea about my rights," said Markus Grupp, 36, who shot one of the most widely viewed videos of the incident. Mr. Grupp recalled an officer asking him for a copy moments afterward.
With smartphones seemingly everywhere, it has become increasingly common for turmoil that unfolds in public – from plane crashes and protests to police confrontations – to be captured on video.
In turn, it is not unusual for authorities tasked with investigating the incidents to seek out any available footage, as was the case when Ontario special investigators asked the public to share video showing Toronto police officers beating a demonstrator at the G20 Summit in 2010.
What is not clear to many people who get a request from law enforcement for their property, such as a smartphone or a copy of video footage they took with the device, is whether they can refuse.
The answer, according to Adam Boni, a former federal prosecutor who specializes in search and seizure cases, is yes, they can.
"Independent witnesses are not under any obligation to assist police," Mr. Boni said. "They have a choice."
Without first obtaining a search warrant, Mr. Boni said, law-enforcement officials can only confiscate a cellphone or view the footage on it if its owner gives what is known as "informed consent," meaning they have an understanding of the nature of the investigation and their role in it.
"Consent can be a tricky thing for some people to understand," Mr. Boni said.
Mr. Grupp recalled his conversation with the officer as "friendly." He said the officer, whom he identified as Constable Michael Choe, asked politely for a copy of the video to be e-mailed to him or, if that was not possible, to meet later at his office where a copy could be extracted from the cellphone.
"He asked a couple of times, 'Is there a way I could get a hold of that?' " Mr. Grupp said. "There was nothing like, 'You have to surrender your phone or give me the footage.'"
The conversation ended, Mr. Grupp said, when another policeman approached and told Constable Choe to end the interview and stop questioning witnesses.
Mr. Grupp said he never followed up with Toronto Police Services, but that he did give officers of the province's Special Investigations Unit, which is probing the shooting and asked him for his footage on Monday, a link to his raw video.
Toronto Police Services spokesman Mark Pugash declined to say whether officers obtained videos from witnesses of the shooting. He said only that, "Any evidence we have has been turned over to the [SIU]."
Mr. Boni, the lawyer, said it should not surprise anyone that investigators would want videos of the shooting.
"They are highly material to the events that transpired, how they transpired, how things were done," Mr. Boni said. "You only have to look at the video once to realize that this is extraordinarily significant evidence."