RAPID CITY, S.D - A Pine Ridge man accused of murder used an ax to kill his sleeping victim and left evidence that tied him to the scene, according to new documents related to his plea deal.

Emery Arapahoe, III is expected to plead guilty later this week to second-degree murder for killing 24-year-old Raymond (Ray) Waters Jr. and to arson for setting the trailer that he was inside on fire in 2017 in Allen, according to his plea deal. Prosecutors will drop charges of first-degree burglary and larceny and also dismiss charges in two separate cases involving assault with a dangerous weapon and assault resulting in a serious injury.

In one of the assault cases, he's accused of attacking a man with a fence post and a heavy blunt object, and then stomping on him April 22, 2017, near Pine Ridge. In the other case, he's accused of kicking a man on Nov. 1, 2017, near Kyle.

Arapahoe, who is now 18 and being tried as an adult at the federal court in Rapid City, was underage at the time of his three cases and originally charged as a juvenile. No matter the crime, defendants in juvenile court can only be imprisoned until they are 21 or 26, depending on their age at the time they committed the crime, Neil Fulton, federal public defender for South Dakota, previously said. Arapahoe faces up to life in prison for the murder and arson charges after his case was transferred to adult court.

Arapahoe messaged Nathaniel Waters, Ray's uncle, early in the morning on Oct. 16, 2017, about meeting up at his trailer in Allen, according to the factual basis document Arapahoe signed. He stole a man's truck in Pine Ridge and arrived in Allen around 5:40 a.m.

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Once inside the trailer, the document says, Arapahoe found Ray sleeping on the couch in the living room. He then grabbed an ax he found inside the trailer and used it to hit Ray "multiple times" on the head and neck, the document said. Ray ended up dying from "multiple traumatic injuries."

Arapahoe used a towel from the trailer to cover the ax, which he put inside the stolen truck, according to the document. He then went back inside the trailer and used materials from a bedroom to set fire to the trailer. He fled in the truck but soon crashed and kicked out the front windshield. Evidence of the murder, including the bloody towel, fell out of the truck during the crash, the document said.

After Arapahoe saw law enforcement arrive, he continued fleeing in the truck to a relative's home near Kyle. He left a boot print with Junior's blood in the truck as well as his own blood after injuring his face.

More details about the case are known from the factual basis document signed by Nathaniel Waters, who pleaded guilty to lying about covering up the killing of Ray.

Law enforcement officers responded to a fire at the trailer around 6 a.m. on Oct. 16 and found Ray "charred," the document says. An agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives found that the blaze wasn't an accident and that it began where Ray was found.

After conducting an autopsy, a forensic pathologist found that Ray was dead before the fire began, and his skull fractures and cuts to his neck were likely caused by an ax. The owner of the stolen truck told Nathaniel Waters that he found the bloody ax inside the vehicle.

From the documents, it's unclear if Arapahoe went to Nathaniel Waters's home knowing Ray would be there so he could kill him. A motive for the killing is also unknown.

Arapahoe's change of plea hearing has not yet been scheduled. Nathaniel Waters is set to be sentenced on Thursday.