SHUBENACADIE, April 23 — Canadian police faced mounting criticism yesterday for using social media and not a provincial emergency alert system to notify the public that a gunman was at large for some 13 hours after he murdered the first of his 22 victims over the weekend.

During the worst mass shooting in the country's history, the Nova Scotia provincial detachment of the Royal Canadian Mounted Police (RCMP) sent a series of tweets to about 90,000 followers warning that there was an active shooter in the area.

But some of the families and friends of the victims said a provincial warning system, which would have sent out text, radio and TV warnings, might have saved the lives of their loved ones.

"I don't use Twitter, and I don't know anyone that does use Twitter,” Nick Beaton said in an interview broadcast by CTV News. Beaton's wife, Kristen, a nurse and mother from Debert, was shot dead on Sunday while on her way to work.

Beaton said he would have never let his wife leave the house that morning had he known the gunman was still at large.

Nova Scotia RCMP Chief Superintendent Chris Leather defended the use of social media yesterday, saying he was "very satisfied” with the messaging, which he said the media helped spread, and that the "communications being provided were the best and clearest information that could be provided.”

Police were in the process of preparing to use the emergency alert system when the gunman was shot and killed by police, Leather said.

The shooter, 51-year-old Gabriel Wortman, began the rampage on Saturday night which continued in several small Nova Scotian towns and ended around noon on Sunday.

Wortman's motive remains unknown. Police have said some of his victims were known to him, but others appear to have been chosen randomly.

Police are still piecing together the timeline of events, Leather said, adding more details could come today. Wortman did not possess a firearms licence in Canada, he said.

Police set up two barriers around the initial crime scene in Portapique on Saturday night, but they did not realise until between 7 and 8 o'clock the next morning that the shooter had disguised himself as an RCMP officer and was driving a vehicle resembling a police car.

There are 22 confirmed victims, but police have cautioned they are still investigating crime scenes, including more than five homes Wortman burned to the ground.

Meghan Nearing, a resident of the area where many of Wortman's victims lived, was home with her son on Saturday night and heard about the shootings, but did not know the gunman was still active when she woke up the next morning.

"There was nothing, no alert, so I thought everything was OK,” she told Reuters, speaking not far from where RCMP Constable Heidi Stevenson was shot and killed by Wortman on Sunday.

"Little did I know he was in my town when I was thinking that.” — Reuters