Jessica Brown, with the Oklahoma State Bureau of Investigation says David Daniel's body was found in his Cotton County Jail cell this morning.
She says it appears he hanged himself, but that won't be confirmed until a medical examiner makes the determination.
Arrest records show Daniel admitted killing his neighbor with a pipe wrench in his trailer because he thought she was stealing things from him.
Then, Speir's body was found in a nearby field two weeks after she was reported missing.
In May, 2010, Daniel drove himself to the hospital in Wichita Falls from his home in Cotton County after suffering a gunshot would to the head in his trailer.
He told authorities he did not know how it happened.
And in 2006, he was shot three times by his brother, Daryl, in Walters, who also shot and killed their father, Donald.
Daryl Daniel is in prison in the Granite State Reformatory.
Last May, a judge ordered Daniel to undergo a competency examination to determine if he should stand trial.
An order finding competency was made last last month and his jury trial for first degree murder was set for this April.
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