Investigators say the water heater for the pool, at the Best Western Plus Blue Ridge Plaza in Boone, was the source of a carbon monoxide leak.
Three people were killed inside one room, including an 11-year-old boy, this weekend.
After an inspection Wednesday, investigators found carbon monoxide was leaking into Room 225 from a pool's water heater in the mechanical room just downstairs. They say that toxic gas was able to leak into the room through a wall-mounted air conditioner and through an opening under the gas fireplace.
"One of the avenues was coming from inside the building," said Fire Chief Jimmy Isaac, with Boone Fire Department.
Investigators believe high carbon monoxide levels led to the death of Daryl and Shirley Jenkins in April and 11-year-old Jeffrey Williams last week. Williams' mother was just released from the hospital. There was no carbon monoxide detector in the room.
"Carbon monoxide detectors need to be a priority," Isaac said. "Through a hole in the building code, it's not required."
Eyewitness News does not know how many people stayed in Room 225 while there were problems with carbon monoxide levels, but police are asking anyone who stayed in the room to contact them.
"While many theories have been confirmed, the investigation must continue to ascertain definitive answers concerning this tragedy," Boone Police Chief Dana Crawford said.