garen wintemute, who's been collecting gun violence data. >> when we think of mass shooters, we thinkfferent archetypes. >> the anomaly is that the shooters are older, in their 60s and 70s. risk for violence, interpersonal violence, goes down with age. so it's unusual to see shooters of this age. >> reporter: between 1976 and 2018, 82% of mass shooters in the u.s. were under the age of 45. >> rates of gun violence increased very rapidly during the pandemic years. we have become angrier. we've become more polarizeded. we have bought guns at a rate without precedent in the nation's history. gun purchasing took off in the first month of the pandemic. and that surge in purchasing just ended in the last couple of months. >> this is a close knit community. what has happened has just been so devastating to us. >> reporter: an especially excruciating loss for chinese american mayor henry lo, who had been preparing lunar new year celebrations, now left reading the names of the dead. >> lynn lee, age 63. shu >> reporter: candles and flowers surrounding the ballroom once full of joy, now honorin

we're joined now by dr garen wintemute from the uc davis violence prevention center really appreciate your time. whenever terrible things like this occur . people are so desperate for answers, but we know that gun violence is a complex. and multifaceted problem. what does your research show as some of the dry main drivers of mass shootings? of mass shootings. um . there are a wide array of causes. some of them are for political reasons. a majority have some sort of domestic violence connection. others may deal with. disputes over employment or housing. the common threads are that semi automatic weapons, those with high capable of accepting high capacity magazines figure disproportionately, um, one of the other common threads and this is really important is that most mass shooters in some way, declare their intentions in advance, which gives us an opportunity to intervene and prevent the shooting from occurring. let me ask you about the situation we're watching unfold here in california so far this year. i mean, obviously, we're dealing with mass shooting after mass shooting yet califo