Note: This story was updated to correctly identify James Hamilton as Brittany Gosney's boyfriend.
James Hamilton pleaded guilty Tuesday in Butler County Common Pleas Court to four charges stemming from the killing of 6-year-old James Hutchinson in February.
James Hamilton, 42, was accused of helping to throw James' body into the Ohio River after the boy was killed and his mother, Britney Gosney, tried to abandon him in a Preble County park. Hamilton was Gosney's boyfriend, but was not James' father.
On Tuesday, in front of Judge Noah Powers, Hamilton pleaded guilty to kidnapping, gross abuse of a corpse and two counts of child endangering.
Powers told Hamilton he faces up to 19 years in prison.
Police said Gosney was pressured by Hamilton to get rid of her children. Records show she had previously tried to relinquish custody of her children but faced "a number of barriers" when she attempted it.
Investigators said Gosney took all three of her children to a Preble County park on Feb. 26. As she tried to speed away from them, James grabbed for the door handle, fell and fatally struck his head, police said.
Gosney and Hamilton later admitted they kept James' body in their home for about a day before driving to the Ohio River near Lawrenceburg and throwing him in the river, police said.
Prosecutors said Hamilton "hog-tied" and gagged James and his two siblings leaving them in that position for several hours.
Gosney pleaded guilty to murder and several other charges on Aug. 16. Her sentencing hearing is scheduled for Sept. 13. She faces 15 years to life in prison.
Hamilton is scheduled for sentencing on Oct. 4 at 8:30 a.m.
Butler County Prosecutor Mike Gmoser said a hearing would be held at some point in which he will argue that Hamilton was a "principal" offender. He said he will prove that Hamilton did more than just go along with Gosney.
James' body has still not been recovered. Searches of the river are continuing periodically, Middletown officials have said.
Gmoser said these guilty pleas on the most serious offenses both Gosney and Hamilton should eliminate any question in anyone's mind that there was a defensive to this.
"It happened because of the evil in the hearts of defendant Hamilton and defendant Gosney," Gmoser said.