Why did the cop not pull me over for speeding?

So I was going home at night, there were barely any cars. I believe I was going 10mph over the speed limit, a cop car next to me (which I thought wasn’t a cop) gave me, what I believe a warning siren screech. So I slowed down and came to a red light, he merged to the lane behind me and waited. It was taking a while... show more So I was going home at night, there were barely any cars. I believe I was going 10mph over the speed limit, a cop car next to me (which I thought wasn’t a cop) gave me, what I believe a warning siren screech. So I slowed down and came to a red light, he merged to the lane behind me and waited. It was taking a while for the light to turn green so the cop just went away. I know cops can check your license plate and see if you have a questionable background. In my case I have no charges, what so ever. So long story short can he still give me a citation without pulling me over?
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