Don Gaines is slated for a court appearance at 10 a.m. on a kidnapping charge.
Investigators say Gayla Roy, who was the mother of Gaines' children, disappeared on Sept. 11. They believe Gaines abducted Roy and choked her before driving off with her to Louisiana.
Roy later regained consciousness during the drive. It was then that Gaines allegedly pulled over on Interstate 10, shot her, and left her to die in the woods.
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The couple had two children, ages one and six years old.
"How could he? You have two boys. You have two sons with my sister," said Felicia Rigmaiden, Roy's sister. "Now you've taken her away from them and you will be away from them. They will be without parents. How could you take the life of someone you supposedly love and been with all these years?"
Roy's father told ABC13 he knew Gaines was the killer since he was the last to see her alive. He said his daughter told him Gaines was taking her home the night she disappeared.
So far, the 30-year-old has only been charged with the federal kidnapping charges. If he is charged with murder, he could face the death penalty.