But there was research, he said, showing that specific policies could reduce the frequency of mass shootings and other forms of gun violence. In Chicago, police and city officials said in a 2017 report that most “crime guns” came from outside Illinois, a state with strict gun laws. “Compared to other states, California has pretty tough gun laws,” said Jeffrey W. Swanson, a sociologist at the Duke University School of Medicine who has studied gun violence. “You might have strict gun laws on the books in Chicago, but Indiana has different gun laws. ”Swanson said the state gun laws that exist could be bolstered by more federal assistance.