If you get a speeding ticket after you've slowed down and get pulled over much later are you innocent?

i got pulled over for a speeding ticket after i slowed down; the cop made a U-turn to come after me. However. I stopped at a red light a block later with the cop right behind me, and his lights still haven't flashed to pull me over. after the light turned green i proceeded; still with the cop behind me, and a half block later he finally pulled me over to right me a speeding ticket. could this be fought in court to prove i am innocent? ( he also did not show me any proof that i was going past the speed limit ) PLEASE HELP!