40 percent of kids who die by suicide use guns. Why do so many parents leave guns unlocked? “Parents may really misjudge or discount their child’s underlying risk,” said Dr. Matthew Miller, study author and professor at Northeastern University, as well as an adjunct professor of epidemiology at the Harvard T.H. Chan School of Public Health. “They have too much confidence in the instructions they’ve given their kids or how they’ve hidden their gun.”