>>10738790 (lb)
It does not change; that's how similar the laws are.
https://giffords.org/lawcenter/state-laws/minimum-age-to-purchase-possess-in-wisconsin/
There's no "intent" needed. They don't even have to prosecute him for "murder". He was 17 at the time of the incident. He obtained that firearm from someone that either broke a law giving it to him, or he "stole" it. He was not hunting, nor was he under supervision of an adult; AS PER STATE LAW.
Look, I hope Lin makes a good case for him; I really do. But Lin's got some homework to do, and he's going to have to work on his jury selection and persuasion skills for this one.