ST. LOUIS -- A Missouri man already serving 20 years in state prison for killing his wife pleaded guilty Thursday to a federal charge expected to add more years to his time behind bars.
Clay Waller, 45, entered the plea to one count of interstate domestic violence. In 2013, he pleaded guilty to second-degree murder in an agreement with Cape Girardeau County prosecutors that allowed him to avoid the death penalty. The deal angered some of his estranged wife's family members.
Waller killed Jacque Sue Waller in 2011 and buried her body on Devil's Island on the Illinois side of the Mississippi River near Cape Girardeau, Missouri. The Wallers were in the process of getting divorced when she went missing and were parents to 5-year-old triplets.
The U.S. attorney's office in St. Louis said the federal plea agreement calls for a 35-year prison term if a judge accepts it at the Jan. 16 sentencing. It would run concurrently with the state sentence, essentially adding 15 years.
Waller's attorney, John Lynch, sought to have the federal charge dismissed earlier this year, believing it was in response to the discovery of Waller's 182-page manuscript detailing the crime and titled, "If You Take My Kids, I'll Kill You!"
But federal prosecutors wrote in July that the charge was to "protect the citizens from a dangerous, sociopathic and narcissistic murderer," the St. Louis Post-Dispatch reported at the time.
Federal prosecutors and Lynch did not immediately respond to messages seeking comment Thursday.
Waller has admitted that he threatened several times to kill his wife if she divorced him. He dug the island grave on May 31, 2011, the day before he and Jacque Waller met with her divorce attorney.
After the meeting, they went to Waller's home in Jackson, Missouri, where he strangled and beat her to death. He took the body by boat to the island and buried it.
A frantic search began for the missing woman, but Waller was an immediate suspect. As part of the plea deal with county prosecutors, he took authorities to the island grave.