You're saying as if it's easy to go undercover into a guarded state building to kill someone without getting caught, being a kid at that. Like you said, it's still before the game story starts, so he doesn't know everything for these parts. He only knows the bits and pieces from the game lore, flavor text and flashback scenes. It's more comfortable for him to setup the scenarios to play out as the game story that he knows inside out for that much much higher success chance.
"he flipped and smacked his head against the wall", no that's not just blackmail, that's obviously some kind of mind control failsafe that prevents leak. Which gave a hint on how Justus manipulated the higher ups, so what use would the evidence do, if he even manage to get it. As for the sword, Harold has been saying it doesn't actually work like what Justus said, so I guess its true effect will be revealed eventually.