Spoilers/theorycrafting crazy person:
I know Ben doesn't remember much of his nightmares/dreams, but he dreamed of Hernandez's death. He had a nightmare of being called to jump down to his death and then start floating down a river...... Not to mention the bridge scene from before. There were quite a few death messages from other characters too. I don't doubt that the suspicious person Zach saw may have had something to do with it (perhaps the white cream colored coat is a clue). However, since Zach heard the call, perhaps so did Hernandez and perhaps that's all it took. I know Chris looks sus with him having been held up, but I know he didn't do it. Since he apparently dreamt up Hernandez's speech, I'm surprised he didn't ask anyone if any of what he heard was true... Did she secretly join a group every year? Was that her favorite location? Was she on the board for its conservation? There was no way for him to have access to that information if it is true. I suppose that would just freak me out more, but at least I'd know I'm not entirely crazy, idk? My name is Ben, and I speak to the dead, or rather, they speak to me.