Guns used in murders have been "decreasing" for 30 years, according to Dr. Garen Wintemute. Dr. Wintemute has spent the last 30 years studying gun violence. “Suicide by firearm is far more common than homicide,” says Dr. Wintemute. "Over the past 30 years, firearm suicides have exceeded homicides even when homicide rates were at their highest in the late 1980s and early 1990s.