Toronto police announced on Thursday that they had recovered a video that is alleged to show the city's mayor, Rob Ford, smoking crack cocaine.

The digital video file was recovered through a forensic examination of a hard drive recovered during an investigation that ensnared Alexander "Sandro" Lisi, a former driver for the mayor, police chief Bill Blair said at a news conference. Police searched Lisi's belongings as part of an investigation into alleged drug trafficking.

In their surveillance operation, police saw Lisi repeatedly meeting Ford. Multiple surveillance images showed a bag or parcel passing between the men with neither acknowledging the other.

Police arrested Lisi on Thursday and charged him with extortion, with the video as supporting evidence, Blair said. He said the video did not appear to be digitally altered or otherwise manipulated. "It appears to be what it is," he said.

Ford has always denied the existence of the video, and Toronto police did not release it on Thursday. It is expected to be played in forthcoming court proceedings.

Blair said the computer technology section at Toronto police made the discovery on Tuesday. H "The file contains video images which appear to be those images which were previously reported in the press," he said. The police chief said Ford appears in the video but he would not describe what the mayor was doing, saying the video was evidence in a court case.

As a result of the police inquiry, Blair said investigators had arrested Lisi and "laid a charge of extortion with respect to the evidence that has been collected".

Blair said that associates of the mayor had been interviewed as part of the police investigation, but the mayor himself had not been questioned or charged. "Everyone has been treated exactly the same," Blair said. "That's the way this works, that's the way it's supposed to work ... no one has been overlooked because of their position."

Ford, who has repeatedly denied smoking crack, engaged in a testy confrontation with reporters who had gathered outside his house Thursday morning in anticipation of the documents' release. He shooed cameramen from his driveway before getting in a vehicle and leaving. He has not commented on the charges against Lisi. Blair said there was never a warrant to search Ford's home.

Police evidence referred to reporting on the story by the Toronto Star and Gawker. Last summer Gawker ran a "crackstarter" campaign to raise money to buy the video, which Gawker editor John Cook had traveled to Toronto to view. Cook reported that it showed Ford smoking from a crack pipe and slurring his words.

The fundraising campaign succeeded but Cook was unable to procure the video and the money went to charity.

At the news conference, Blair said he was "disappointed" by what he saw, although there was not enough evidence to charge Ford. "It's a significant issue, and I think it's a significant issue of public concern," Blair said. "And I think that is a problem for our city."