My brother is convinced he's been replaced

My brother used to have a very good friend called Jack and they went on a roadtrip together this summer. They’ve been friends for years and everything seemed fine, but when they got back my brother just started to act really strange. He’s become a bit of a loner and he never leaves the house, and he even stopped going to work. He also destroyed his phone and doesn’t want to contact Jack or any of their mutual friends ever again. He told me that something really disturbing happened on that trip and that he can’t tell me all the details, but that Jack was agonisingly tortured to death by some psychopaths while he barely survived by escaping. He also said that the only reason he came back alive was that the people who caught them wanted him to replace Jack. He told me that they forced him to watch Jack being brutally tortured and disfigured while they instructed him on how to behave as Jack, talk as Jack and answer as Jack would. He said that he was forced to watch Jack die a slow death and then he was stitched and glued together again to make him look exactly as he did before. He said there was a bunch of people at that place, men and women, who seemed to have a lot of fun while an innocent man was screaming his lungs out while being disfigured beyond recognition. He said that they never tried to kill him, but that they made it very clear that they would come after him and kill him if he didn’t behave as Jack. He told me that he’s been fearing for his life ever since he came back, and that he’s constantly paranoid about these people coming after him. He said that he’s been in complete shock and that he doesn’t know how to react or feel, and that he should probably get some therapy to deal with this trauma, but that he doesn’t know where or who to ask for help. So he’s in a very bad place right now and barely talks to anyone.<br><br>It’s really terrible to see him like this, and I do obviously believe my brother, but I’m also very confused, because I called Jack not too long ago to ask if he wanted to hang out, and he seemed completely fine. I told him about my brother, but he said that he doesn’t know what he’s talking about. He’s a really nice guy, and it doesn’t really make sense, but I don’t know what else to say. Maybe I’m just very gullible.