Houseboat deaths appear accidental

HAMBURG -- An investigator says four adults whose bodies were found over the weekend on a Mississippi River houseboat may have been victims of carbon-monoxide poisoning.

Mark Wagner of the Illinois Department of Natural Resources' conservation police says the two men and two women had been camping on an island just north of Hamburg. The boat was tied to the island when their bodies were found Sunday.

Wagner says the investigation is continuing but carbon-monoxide poisoning is suspected.

Autopsies are planned.

Calhoun County Sheriff Bill Heffington says there were no marks on the bodies that indicated foul play. The names of the dead haven't been released.

Hamburg is about 50 miles northwest of St. Louis.