The bodies of Richard and Clair Smith and their children, Ben, 9, and Aaron, 1, were found Sunday afternoon in a single bedroom in their house in Pudsley, Leeds, The Daily Telegraph reported. Police broke in after being notified by concerned relatives they had been unable to reach the family.
Investigators initially believed the family had died from carbon monoxide poisoning but later determined it was a murder-suicide, police said.
The family had been living in the house for just over six months. Neighbors said they saw Smith washing his car Sunday but had not seen his wife and children during the weekend.
"I find it very hard to believe. He thought the world of them," Gary Tempest, Smith's cousin, told the Telegraph. "I've known Richard all my life. There's never been any bad things, arguing or anything."
Tempest said Smith, 37, and his wife, 36, both had good jobs.