FREEDOM, Maine (AP) — Two people died and two others were treated for carbon monoxide poisoning at a Maine home previously busted for an illegal marijuana grow operation, officials said Tuesday.

Freedom Fire Chief Jim Waterman said his agency was alerted to a possible gas leak shortly after 6 a.m. and discovered lethal levels of carbon monoxide inside the home. Five people were inside when firefighters arrived, and two of them were dead, he said. Two others were taken to hospitals for treatment.

In May, law enforcement officials raided the home and seized more than 1,900 marijuana plants from the property, which included several buildings. The bust fit with a trend in Maine of criminals trying to take advantage of the legalization of marijuana to fly under the radar to produce marijuana that’s sold in states where cannabis is illegal.

On Tuesday, firefighters who discovered lethal levels of carbon monoxide traced it to a pipe from the propane heater that had become disconnected, sending fumes into the house, Waterman said.