Even if someone close to you shows disturbing signs of wanting to do acts of violence to and signs of hatred of women, immigrants, Muslims, Jews, Blacks, Hispanics/Latinos, rich people, "Conservatives", "Liberals", many of us won't act to report them to police, get them mental health help, or prevent them from getting or possessing weapons. Denial of the truth of that person, fear of admitting they know someone with this problem, fear of losing them in their family, breaking up a family, fear of violence upon them all make it difficult to stop possible mass shooting or other violent acts. Many of those in mass killings take time to make their plans, what weapons to use, how to get away with it. They may post, as often seen, comments or postings on websites or in personal writings their anger and plans.
Still, the advice of 'see something - say something', like we are told to watch our for bombs or certain behaviors in public, could make the difference of prevent such mass killings. There was a news report earlier this week where a Grandmother turned her grandson to police due to disturbing signs of possible acts of violence by them. Tough love indeed, difficult to do but the right thing for all involved or could be.