Graves is traumatized by the time he spent as Grindelwald's captive. He stole his face, and now he can't look at himself without seeing Grindelwald staring back. People now flinch when they see him or they look away. And what's worse, people expect he will just bounce back to being unflappable gruff Mr Graves and clean up the massive mess Grindelwald left behind. One day, when he is feeling particularly low, he grabs a knife or a razor and cuts up his face badly. That's how one of his co-workers finds him. After that they finally get Graves some help.

I would like someone from MACUSA (Picquery, Tina, a random auror or even Abernathy) to find Graves like that, but if you want it to be Newt or Credence, it's up to you.