Sufficient grounds for the stop, since, at the border, a consented-to scan of the trailer had revealed it to be largely empty, but a safety seal was evident on the doors; additionally, the stop was within fifty miles of the border.
Being told that he would be free to leave after the canine unit had checked the trailer was insufficiently custodial to exclude the non-mirandized statements in the interval.
Roving stops by Immigration are justified whenever there is reasonable suspicion of any criminal activity.