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 JACKSON, Mo. (AP) _ A southeast Missouri man accused of killing his estranged wife has pleaded not guilty.

KFVS-TV ( ) reports that Clay Waller of Jackson entered the plea during a hearing Monday. His next hearing is scheduled for Oct. 22

Jacque Waller disappeared in June 2011 after the couple met to finalize divorce plans, and her body has never been found. A judge ruled after a hearing in July that there was probable cause for the case to proceed.

Clay and Jacque Waller had triplets who are now living with Jacque Waller’s sister. Clay Waller is already serving time in a federal prison for threatening his wife’s sister over the Internet.

See More Coverage of the Waller Case
Clay Waller to Be Tried in Wife’s Presumed Death
Clay Waller Hearing Turns Violent
Vigil Held on 1-Year Anniversary of Missing Mother