Smith said Alaska Psychiatric Institute issued the finding after examining Whisler.
Whisler is facing serial rape charges dating back to 2002, a few months after he moved to the state.
He was initially arrested in January on charges he sexually assaulted a woman after taking her stargazing on Lazy Mountain. Officers investigating the woman's complaint uncovered five other women who reported being pawed or assaulted by Whisler and he now faces 15 counts of first- and second-degree sexual assault.
Whisler was convicted in 1999, while he was a teenager living in Oregon, of three sex-related offences against two 9- and 10-year-old girls.
He served 18 months in a sex-offender treatment program and the remainder of his sentence in the custody of his parents. He was released when he turned 18.
His parents, Dean and Tina Whisler, fought the Oregon charges. They said their son has Klinefelter's syndrome, a genetic disorder that causes him to misread social cues, and that he didn't understand what he had done.
The Whislers in February said the charges their son now faces were brought by a group of friends who are lying in an attempt to get their son in trouble.
Smith set a January trial date for the case. Whisler is currently being held at Cook Inlet Pre-Trial Facility in Anchorage.
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