As far as influencing law enforcement doctrine and tactics, IMHO there are actually four major incidents.
1. Lots of people have never heard of the Norco shootout in California. This is a riveting account of a running gun battle with armed bad guys. The cops were armed with revolvers, two reloads and pump shotguns. The BG's (IIRC) were armed with an AR15, a HK91, and multiple handguns.
2. The infamous FBI shootout in Miami woke the LE community up to more modern equipment that gave officers more immediate firepower. After that shootout, the emphasis was on replacing revolvers with semiautomatic handguns. Research and testing done as a result of that incident gave birth to one of our most popular cartridges to date, the .40 Smith and Wesson.
3. The Onion Field incident also caused a major shift in law enforcement training and doctrine. This one was where two officers were abducted; one was executed in an onion field; I believe the other one escaped.
4. However, the second single most important incident concerning law enforcement officers--and another incident causing a major shift in training, doctrine and tactics--was the Newhall massacre. Police officers pulled over a car load of armed killers. When the shooting stopped, four officers laid dead. This incident gave us our current procedures for the felony (hot) stop and also placed a major emphasis on officer safety.
Hiding in plain sight...