By selective, I assume you mean prosecute one individual and not another. That’s not what I mean.
What I mean is that officers can watch you die and then start the process of prosecution against whom harmed you.
That’s why the reward was so small in Uvalde, likely. The officers could have waited for every kid to shot dead and then enter the building to begin the process of prosecution.
https://www.findlaw.com/legalblogs/law-and-life/do-the-police-have-an-obligation-to-protect-you/
That’s one interpretation.
Mine is that the state ensured that it got the outcome that in wanted in the Uvalde case.
And the difference in those outcomes is telling.