YERINGTON, Nev. -- An investigation into the deaths of four people at a motel room in Yerington indicates they were victims of carbon monoxide poisoning from a swimming pool heater.

Police said there were signs the four -- a Yerington man and three people from the San Francisco Bay area -- had been drinking, but there was no trauma, no weapons and no indication of drug use.

Mason Valley Fire Protection District Division Chief Scott Huntley said tests on Monday showed an elevated level of carbon monoxide in the room at the Casino West Motel.

While initial reports said the room has a gas heater, he said that was incorrect -- the room heater is electric. Huntley said it appears that the lethal fumes came from a malfunctioning swimming pool heater located beneath the victims' room.

The Yerington man was identified as Phillip Doll, 26. The other victims were Donna N. Vega-Robles, 30, San Pablo, Calif., and Juan Pablo Chavez, 27, and Veronica Espinoza Chavez, 20, a husband and wife from Richmond, Calif.

Yerington Police Lt. Darren Wagner said a maintenance man answered a complaint on Sunday of water leaking into the room below, went upstairs, saw bodies in the room, about two inches of water on the floor and got no response when he knocked and called. Water was running underneath the closed bathroom door.

One female victim was in the bathtub with the water running, and a male victim was against the bathroom door, which had to be forced open.

The Nevada Department of Public Safety Investigations Division and the Forensic Investigations Unit from the Washoe County Sheriff's Office are assisting in the investigation.