What you can and must do to help stop mass shootings

Why it matters: FBI behavioral research has found that 80-90% of mass shooters "leaked" warning signs: "Watch out on Tuesday."

"Law enforcement is likely to be the last to hear," said Schweit, now a workplace-violence consultant.

• "It's not uncommon when we interview people for them to say: 'He's always been like that, but he's never done anything like this before.'"

"The biggest ace in the hole we have for prevention is people listening to the people around them," she added.

• "Employees and friends need to report concerns not because they want to get them in trouble, but because they want to help them out."

Retiring Rep. Will Hurd (R-Texas), a former CIA undercover officer, told Wolf Blitzer on CNN that threats are often "shared on social media in a way that can help tip and cue federal law enforcement":

Screenshot it.  If you're looking at it on your phone, screenshot it, and then do a search for [your] police department. There's guaranteed to be an e-mail where you can send these kinds of things and then attach that screenshot to an email and send it to local police.

You can actually find the FBI's phone number in the phonebook. I don't know if people still use phonebooks, but that is something you can go on the internet and find that as well.