I typically avoid these types of threads but I'll try to clarify a few things in general (not specific to this shooting, let the investigation take its course)
Officers need probable cause to initiate ANY traffic stop. ie speeding, running a stop sign or any of the other millions of laws on the books (as it was suggested by the mother this one was for an air freshner, possibly obstructed view?) Once the stop is initiated, the officer investivates for further crimes. DUI, open container, warrants, valid license ect. I think most here will agree that is the way the system should work.
If the the suspect then resists, lies about identification, or flees, that would then be additional charges stemming from the initial traffic stop.
So, as an example from my past as an officer. I went to stop a speeding vehicle. The driver didn't stop and I pursued. He pulled into his driveway and tried to run inside. Fight ensued and I got a minor injury. He got inside his house. I got adfitional units and made entry and arrested him (he gave up seconds before the K9 was released). He got multiple felony charges. Resisting, battery on LEO with injury, fleeing, possession of narcotics (drugs left in plain view in the vehicle he bailed from) and a speeding ticket. He probably ditched additional drugs in the house before his arrest.
Also keep in mind most officers know the drug players and general bad guys on their AO. I have seen many times in my area where LEO sit on bad guys waiting for a reason to stop them. That could be the case with the original post in this thread, but thats my guess.
I'll be happy to discuss further as long as its a civil conversation. The face of this case seems bad and the lastest video does seem like the officer really screwed up. But let the investigation take its course before jumping to any conclusions.