Originally Posted by
Badenoch
Pre-clearance facilities in Canada are not under the control of American authorities. A person who commits a serious crime in a pre-clearance facility in Toronto will be arrested by Canadian police and prosecuted by the Canadian court system. Similarly a person who commits a serious crime between getting off the plane and being cleared by customs in any country will be prosecuted by that country.
... not limited to
serious crimes.
If the OP's premise had any basis in fact, I'd never have seen CPB authorities on the jetway as I disembark, with dogs, looking for selected arriving passengers.