“So, if I am caught speeding and another car speeds by not apprehended. Assuming I have it documented I can use that to get out of the ticket?”
No, because “selective prosecution” is about prosecuting people who HAVE been apprehended differently. It’s not available just because police can’t catch every criminal. So you’d have to change your example to something like two people both got pulled over for the same offense, and the police arrest and charge one but not the other. In that case, you might be able to use the “selective prosecution” defense.
“Can’t the prosecutor say “Prosecutorial discretion”?”
Sure. Not every defense is automatically successful, and there are counters available to just about every defense. But to make a successful argument for “prosecutorial discretion”, the prosecutor must then go on the defense, and demonstrate that their discretion wasn’t arbitrary or improper. So you’re already in a better position than you were before, when you were the one on the defense.
Thanks for the explanation!