A family of five was found dead in the northwestern U.S. state of Oregon on early Tuesday morning, in an apparent domestic-related murder-suicide case, local authorities said. A sixth death is also being investigated.

A mother and her three children were found deceased at their house in the northeastern area of Salem, the capital of Oregon, at around 5:30 a.m. local time on Tuesday morning. They were discovered after a neighbor called 911 to report smoke coming from the residence, which is located in the 2800 block of Fisher Road Northeast.

"As firefighters were attending to the fire in the residence, they located the three young children and the woman and removed them from the house," said Lieutenant Dave Okada, a spokesman for the Salem Police Department. "Evidence located at the scene indicated that the victims died as a result of homicidal violence and firefighters requested the Salem Police Department respond."

Okada said an initial investigation led detectives to identify the husband of the woman, who is also the father of the deceased children, as a person of interest. He was later found deceased in a vehicle near Cottage Grove, a city about 78 miles (126 kilometers) south of Salem, in what appeared to be a suicide.

Meanwhile, detectives are also investigating the death of a man whose body was found beside the roadway on Fisher Road Northeast, just several hundred meters (yards) from the house where the mother and children were killed. Police said the body was discovered by a delivery driver who notified police at 4:23 a.m. local time.

Okada said detectives are treating the family deaths as a domestic-related murder-suicide situation. It is unclear how the sixth victim died, or if he is related to the murder-suicide case, but the scene was being treated as a separate investigation as of late Tuesday.