Unknowns in Ohio shooting include: Did he target his sister?

DAYTON, Ohio (AP) — As authorities in Ohio try to pin down a motive for the weekend's second U.S. mass shooting and dig into the slain shooter's life, what they find might also help answer another big question looming over the tragedy: What, if anything, could have stopped it?
Police say the gunman was wearing a mask and body armor when he shot and killed his younger sister and eight others after the pair had arrived together with a friend earlier Saturday evening at a popular entertainmen