The man accused of kidnapping and raping Jaycee Dugard has issued an apology in a jailhouse letter and referenced "a sexual problem believed to be impossible."

In a letter to Sacramento's KCRA-TV received Thursday, Phillip Garrido said he wanted to "apologize to every human being for what has taken place."

Garrido and his wife, Nancy, have been charged with abducting Dugard from a South Lake Tahoe bus stop in 1991 and holding her captive for 18 years in their backyard.

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Both have pleaded not guilty.

Garrido's lawyer, Susan Gellman, says he is expressing genuine remorse. She also says there are "obvious issues" over whether he's mentally competent to stand trial.

In a previous letter to the television station, Garrido alleged that Dugard's civil rights were being violated during questioning with authorities.