As the fallout deepens from the catastrophic mass shootings in Lewiston, Maine, that left at least 18 people dead and many wounded, questions are being asked about how an army reservist who had threatened violence and was kept under observation this summer for erratic behavior was allowed to be in possession of a deadly semi-automatic rifle.

Studies have shown that red flag provisions do have the potential to intercept weapons before mass shootings occur. April Zeoli, director of the policy core of the University of Michigan’s institute for firearm injury prevention, has looked at six states with red flag laws.

A review of almost 7,000 extreme risk protection order petitions, brought mainly by law enforcement in those states, found that nearly 10% involved some kind of mass shooting threat. Of those, 50%, or 330 petitions, involved what Zeoli called “maximum casualty threats”, where the person showing the erratic behavior appeared to want to kill as many people as possible.

Dr. Zeoli spoke with The Guardian about what data shows around the impact of ERPO laws