When officers arrived, they found a car running in the garage. Investigators believe the sisters came home last night, parked the car in the garage and shut the door.
However, the car was still running, letting carbon monoxide build up inside.
Investigators believe the women died overnight. They were pronounced dead at the scene.
Neighbors identify the homeowner as Helen Pompeii, a widow who lived in the home for many years.
"She was a nice woman. Kind of kept to herself," said neighbor Nick Walsh. He discovered the tragedy when the carbon monoxide detector in his home went off.
"The car was in there running with the garage door shut," Walsh said. His brother went inside the garage and turned off the car.
"He said he could hardly breathe in there," Walsh said. The men banged on the door, but there was no answer.
Helen Pompeii was found dead in her kitchen. Her sister was found dead on a couch in the living room.
Police say the home had working smoke detectors, but no carbon monoxide detectors.
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