He did have “signs” to some extent.

His grades were slipping, he wrote that he was going to “make my mark in the USA. Something’s definitely wrong with me”, He wrote about his self harming, people around him noticed he wasn’t himself etc.

The “make my mark in the USA” writing seems to be a big red flag.

Also on the Gracie strong foundation website written by the victims parents states:

“Following the tragedy, it became obvious that if the people around the shooter, or even the shooter himself, had not been afraid to speak up, the senseless violence he committed could have been prevented” which indicates people close to Nathaniel knew something was not right with him yet chose to not say anything.