There were mentions in a few news reports in the first couple of days after the story broke that Karr was being held in Thailand "on unrelated sex charges" (with no additional detail). But subsequent news reports all said that the timing of the arrest had been at the behest of the Colorado investigators, and that the grounds for the arrest were US charges. A lot of stuff that was publicized in the first couple of days, as Thai officials admitted they weren't sure about some of the things they had reported Karr had said (re drugging JonBenet, picking her up from school, etc). It seems the Thai authorities are pretty loose-lipped, and that could well account for these early references that seemed to imply Thai sex charges.
A Reuters report on Aug. 17 (the story broke on Aug. 16) said he had been "detained in Bangkok on a U.S. warrant seeking his arrest for murder, kidnapping and sexual assault" http://www.freerepublic.com/focus/f-chat/1685494/posts .
By Aug. 19, Boulder DA Mary Lacy had spelled this out in a press conference:
http://www.freerepublic.com/focus/f-chat/1686531/posts
"At a news conference Thursday, Lacy indicated that "exigent circumstances" forced the arrest of Karr to occur before she would have preferred. She did not disclose any of the evidence she has that could tie Karr to the crime. She added that an investigator from her office was dispatched to Bangkok on just a few hours' notice before Karr was picked up at Boulder's request."
Also on the 19th, a Thai publication gave details which made clear that Karr was being handled by immigration authorities (detained at an immigration bureau center, visa cancelled, etc.) http://www.freerepublic.com/focus/f-chat/1686612/posts and makes no mention of any current or former charges for crimes allegedly committed in Thailand.
Frankly, the only place I ever saw any specific claim that Karr was facing criminal charges in Thailand was in FR posts, accompanied by speculation that fear of the Thai justice system was Karr's motivation for babbling about JonBenet and getting extradited.
Thanks for that.