threats, we will be out there in high visibility. reporter: the fbi and homeland security warning about nonspecific chatter that they feel could lead to lone violence. a gunman killed 12 and injured dozens when he opened fire during a batman film screening in aurora, colorado. grieving parents call joker a haunting reminder. how are other survivors of not just aurora but other gun violence going to react to being triggered again? reporter: but some fans aren t afraid. it doesn t bother me. i was planning to see the movie anyway. reporter: this is the kind of movie fans would dress up for. but security concerns have prompted some major chains to ban costumes. joker reveals the background of the villain, a man who finds relief in violence. brian lowry says among the parallels with real life attacks, he faces female