I just got an e-mail from my brother who lives in Columbus, confirming that neither he, nor his wife, nor his wife's brother were at the Damageplan show where this happened. I am so relieved. All of them are hard rock/heavy metal fans, but they had other things to do that night. My brother said that our bro-in-law would almost certainly have attended if he hadn't been studying for finals.
That's a major weight off my mind. And on some level, so is the fact that the s.o. is no longer a touring rock musician! I'm not the sort of person who'd ever try to limit what I or my loved ones do because of fear, but yeesh. There are some bona fide crazy people out there.
Here's a follow-up report. Very unnerving.