He didn't use radar, according to what he said road-side with us.
He passed us while we were taking pics of that meadow and mountain range about 2 miles earlier, and probably was in the act of turning around on a side road to establish a speed trap and saw us go by.
Then he passed me at triple digits with his siren off but lights on (when I was just about to pass a little pickup truck between you and me, scaring the bejeezus out of me in the process), put his siren on for you, pulled you over and then instructed me to join you guys.
I was more than a bit irked by the way he passed me.