CHARLOTTETOWN -- Teens who died last month after a fire erupted inside an abandoned building in Charlottetown had set the blaze to keep themselves warm, police said Monday.

The city's police department issued an update on the investigation into the March 29 fire that killed three teens, saying while fire officials have an area of origin where the fire began, they don't know what ignited it.

Investigators said four boys were driven by a friend from Montague to Charlottetown, where they socialized with other friends at a shopping mall before hanging out at a vacant building.

Deputy Chief Gary McGuigan said the boys started a fire at some point that night to stay warm before they fell asleep.

"We have evidence that supports that there was an open fire in the building when the victims went to sleep," said McGuigan.

McGuigan said the last correspondence from the boys came in a text message that one of them sent to a friend at 2 a.m., about 3 1/2 hours before police and firefighters responded to the fire. Police do not suspect foul play.

He said the building was frequented by teenagers and all but one of the four boys had been there before.

The bodies of three teens -- Joseph Reeves, 19, Brandon MacKinnon, 16, and 15-year-old Kenneth Irving -- were found inside after the fire.

One of the boys managed to escape and was rushed to a Halifax hospital. McGuigan would not provide details about his condition, but said he has been released.