A variety of tricks the English Crown was fond of at the time were expressly barred in our Constitution. That is one reason treason is so strictly defined. English law on the matter was so 'flexible' the claim 'a man who said Godspeed to someone engaged in a treasonable enterprise might find himself on the scaffold' did not exaggerate by much. The people who drew up our Constitution had been at risk of the treason laws of England, and many had been outright criminals in violation of the excise even before the Revolution. They wrote in what they'd have liked the law to be while they were engaged in breaking it. People who complain about criminals getting off on technicalities fail to appreciate the true bias of the document such decisions are based on. We are not a law abiding people, never have been, probably never will be.
So far as I am aware, people caught for a crime after some delay are tried and sentenced under the law in effect at the time of the crime, not what it may be at the time of their arrest and trial. At least so long as the offense remains a crime at the time of the arrest. In Illinois, for instance, if there were some old warrant out for possession of a half ounce of marijuana, and some zealous officer performed an arrest based on it, the charge would be dismissed. Possession and sale of a dozen pounds could still be brought to trial, as that remains illegal to this day (or at least I believe it is, it's not something I have had any occasion to check)....