Probably the absolute bare minimum. It will be interesting to see the evidence authorities have on this guy that they are withholding from the general public once trial starts. I bet they have a ton of evidence in this guy.
Discussion
Shit, we already know they have fingerprints and DNA matching him to the 9mm shells left at the scene of the crime, as well as on a water bottle and protein bar they have him on camera buying at the local Starbucks right before the shooting. Combined with his handwritten notes explicitly admitting to the attack, and secondary evidence such as the video tracking him to the hostel, and the fake ID he had in his position that was also used to check in to the hostel, claiming he's not the guy is going to be a very tall order in court. Claiming he didn't do it already sounds preposterous, and we still haven't seen all the evidence.