Read more about this story from CNN affiliate KOIN.
(CNN) -- Investigators on Monday will return to the scene of a fire at a one-story residence in Vancouver, Washington, that killed six people on Easter morning.
Authorities had initially said two people died in the fire about 1:30 a.m. Sunday. On Sunday evening, Vancouver police revised the number saying firefighters found the additional bodies after sifting through the rubble of the home.
Investigators do not yet know what caused the fire, but have not ruled out arson. Neighbors told CNN affiliate KOIN they heard a loud explosion just before the home went up in flames.
"My fiancee ran up, beat on the car trying to set the car alarm if there was one. Tried to run up to the door. But the glass had blown out at the front of the house about 20 feet and it covered the whole entire front of the house," resident Jon Himes told the affiliate. "So she couldn't even get up there to bang on the door."
Police spokeswoman Kim Kapp said arson investigators and the department's Major Crime Section were looking into the fire, and has called in agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives.