Beyond the civil liberty concerns about monitoring people through their gadgets, Randazzo said, there’s the problem of false positives.

Even if the technology could be developed, such a program would likely flag tens, or hundreds of thousands, more possible suspects than actual shooters. How, she asked, would you sort through them? And how would you know you were right, given the difficulty of proving something that hasn’t happened?

Most concerning, she said, is that the proposal is based on the flawed premise that mental illness is directly linked to mass shootings. “Everything we know from research tells us it’s a weak link at best,” said Randazzo, who spent a decade conducting such research for the Secret Service and is now CEO of a threat assessment company called Sigma.