I think Luigi has always been open that he did it. Remember the whole "your coverage of this event has been completely out of touch"? If he was an innocent guy scooped off the street, I doubt he'd give a fuck of how the media was reporting on Brian Thompson, kek. Realistically, what media reaction was he expecting?
From what we know of, the evidence was overwhelming. We have the ID with his face and fake name, CCTV footage, his DNA on the backpack and candy wrapper, ballistic evidence matching the bullets to his ghost gun, his writings and whatever eyewitness testimony that won't be revealed until the trial. I imagine the secretary he smiled at will be called in to identify him, and Luigi's so distinctive looking that you wouldn't confuse him with anyone else. He could have gotten jury nullified, but I think Seidemann and the federal prosecutors are very aware of this possibility and are going to make sure leftists, most very young women and people with past bad experiences with health insurance aren't going to be on the jury. He was screwed the moment he pulled that trigger.