The bodies of David Hopkins, 56, and Betty Stroppa, 59, were found about 7 p.m. PT Sunday in the Edmonds area.
Investigators say the couple may have been killed by a carbon monoxide leak from a propane-powered generator.
"It would appear, after interviewing the neighbours, that one of his neighbours and Mr. Hopkins were replacing part of their propane generator on Friday, at which time the air vent from that generator was closed," said RCMP Cpl. David Reid.
"It would appear that it was not reopened, so that would mean that when the generator was running, the propane leakage was basically funneling carbon monoxide inside the trailer."
Carbon monoxide detector important
The Canada Safety Council says carbon monoxide poisoning remains the leading cause of fatal poisonings in North America. Exposure to high concentrations can cause death in just a few minutes.
Raynald Marchand, the council's general manager of programs, said carbon monoxide is an odourless, colourless gas, and the best way to prevent poisoning is to have a properly placed detector.
"Where you need to have it really is in the master bedroom where the parents are sleeping, because it's usually when you sleep that this killer comes along and you don't notice it because you're sleeping."
Authorities also recommend checking all appliances regularly and ensuring living spaces have a steady flow of fresh air.
The most common symptoms of carbon monoxide exposure are:
- Shortness of breath.