Here's my take. The DOJ's case against the Minnesota shooter will go first-

[Ocelot II]

2. I don't think that will happen. The federal statute says

it's a federal crime to commit murder with a firearm if done in the course of committing another federal crime. Which other federal crime is he accused of? If someone commits murder while engaging in or attempting to commit a federal crime like bank robbery, kidnapping, or drug trafficking, it can be prosecuted under federal law. Murders of federal officials or that occur on federal lands, military bases, or other federal property fall under federal jurisdiction. Murders involving interstate activity can be federal. I'm waiting to hear what federal crime is involved here.

I doubt very much that even if the feds prosecute him he'd be pardoned. Trump used the pardon power to obtain bribes. Pardoning the 1/6 assholes was his way of encouraging them to keep being violent MAGA assholes on his behalf. Pardoning his rich donors tells them they can keep doing their fraud with impunity as long as they keep giving him money. He won't bother with some impoverished murdering wacko cop cosplayer, even to own the libs. There's nothing in it for him personally, which is all he cares about. And he's all hot for more death penalty cases.