Are you saying he was not given immunity from prosecution?
If he was, I find that revolting.
He was given "use immunity" for his testimony, which simply means the prosecuter can't use his own words against him.
If he goes to a civil case and, in the civil case, says he was driving the van, the prosecuter will be able to arrest him for the drugs. He was never given immunity for the drug smuggling, only immunity for the use of his words.
However, there was no way to prosecute him for the drugs without his words. Why? Well, there were three agents who were involved in the pursuit -- Campeon, Ramos, and Juarez. However, all the agents said they could NOT identify the man. They didn't apprehend him. They didn't file a valid report about the shooting. There was no physical evidence in the van linking the man to the van or the drugs.
When the two agents testified that they could NOT identify the man who ran from the van, that ended any chance of prosecution. You can't prosecute a man if you can't even identify him.
The only reason we know that THIS GUY is the guy they chased is that HE CAME FORWARD. He did so only because he had use immunity, and that immunity was ONLY for the testimony he gave, not for the underlying crime, or for any other things he might say at any other time.
Most times when police are convicted of brutality, it's because they beat up a bad guy. Police rarely beat up innocent people. But they do use excessive force against bad people, and prosecuters grant immunity or reduced sentences to bad people to get testimony against cops.
That's because we consider it a much more serious problem when police take the law into their own hands. That is true in this case as well -- no illegal is EVER going to surrender if they know they could be shot anyway.