Police asked that details of the letter provided to the media not be released.
"The letter had things they (detectives) were already aware of, but some of it had things that our investigators will check out," Wardlow said.
Mitchell's husband, Teddy Mitchell, 56, was out of town at the time of her death, one of his sons said.
Police said Teddy Mitchell is known to be involved in illegal gambling, and his online profile on an Internet gambling site mentions poker tournaments in which he competed.
Police have learned Teddy Mitchell is a bookie, someone who illegally collects bets on sporting events, authorities told The Oklahoman.
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HOW TO HELP
Anyone with information can call the homicide tip line at 297-1200.