Eh, “secret service agent” detail to the president is quite a stretch to reach “police officer” or patrolman. It may be those reports surfaced before Officer Tippett was shot, that was a couple hours later wasn’t it?
You don't think the US media is capable of making sizeable stretches during chaotic events? Kennedy was shot around 12:30 p.m. Tippit was shot around 1:15 p.m. so while not simultaneous, it was within the same hour. I'd imagine reporters monitoring police radios could have very easily connected/muddled the events.