DONIPHAN, Mo. (AP) -- Three people have been charged with killing an elderly southeast Missouri couple whose bodies were found in their burned-out home in June 2010.

Charges of first-degree murder and armed criminal action were filed Tuesday in Ripley County against 47-year-old David Youngblood; his 19-year-old daughter, Chantale Youngblood; and 19-year-old Keith Boyles. All are from Doniphan.

Authorities initially believed Loyd and Irene Piatt died when their Doniphan area home caught on fire. But they discovered the couple had first been shot after a similar incident a month later.

The three suspects already have pleaded not guilty to murdering 81-year-old Edgar Atkinson and 69-year-old Bonnie Chase, whose bodies were found in their burned home in July 2010.

Calls to the offices of attorneys for the three defendants were not immediately returned Tuesday.