Mason City, IA – Officials say two Mason City residents have died of apparent carbon monoxide poisoning.

The Globe Gazette reports Monday that 67-year-old Thomas Jimenez and his 80-year-old wife, Carmen Jimenez, were found dead just after 4 p.m. Saturday in their home. Police had checked on the couple after a relative called out of concern for not hearing from the couple since Thursday.

Police found the doors locked and had to break in. Once inside, police discovered the couple lifeless.

Police say carbon monoxide levels were strong enough that one officer was taken to a hospital, where he was treated and released.

Fire Chief Bob Platts says the situation remains under investigation.