Police and other emergency personnel are allowed to drive over the speed limit without lights or sirens if they are responding to a non emergency. When I was working EMS we had 3 levels of response. Level 1 was lights and sirens, 2 was quick but to lights and sirens, 3 was drive normal. So it's possible he was on a level 2 response somewhere, then when he saw you following him at a high rate of speed he told someone else to respond to the call so he could stop you .

Funny little fact too. Technically there's still a law on the books that says mail carriers are allowed to run red lights