The agent claims that he opened fire in response to an "aggressive move" by Noriega.
In other words, the timeline the agent asserts is: - While in plainclothes and an unmarked car, I observed someone drive into a school parking lot. - I thought he might be the suspect, but wasn't sure. - I decided that "might be the guy, but if I'm right he's a dangerous armed drug dealer, let's hope so" + "next to a school" + "I've got no visible law enforcement markings on my car, this'll look like a carjacking" = "dont' be a pussy, takehim down, what could go wrong?". Anyways, he's Mexican so his car is probably full of coke and guns. I smell a promotion! - I blocked his vehicle with an aggressive blocking maneuver. - He fled my unmarked car that out of nowhere pulled up in front of him with screeching tires, thereby proving his guilt. - I opened fire. - I am a hero. - Noriega continues to flaunt his disregard for my authority, by flagrantly failing to be the narcotics trafficking fugitive we were looking for.
Again, that's the [slightly editorialized] version of events per the ICE agent.