Re: Denver OC. By their own law, they prohibit
A) Open Carry
B) Concealed Carry
C) Unless the person has a state CCW permit in which case A) & B) are invalid.
That is essentially how their law reads. Will you still get arrested, probably. You'd be the test case to break the 3/3 deadlock on Denver OC. My lawyer and I sat down back when he took my case on and we went over that statute, as he noted by the letter of the law you would be legal, but practically speaking you'd be in my shoes with a pending court case, and potentially a suit against the city.
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As for Thornton, oh, they'll arrest you for OC as well when you violate the PC law of "too soon" after Aurora - what it says, how long that is etc, no one can say because they can't find it on the books.