Guns used in murders have been "decreasing" for 30 years, according to Dr. Garen Wintemute, pictured above. Dr. Wintemute has spent the last 30 years studying gun violence. 

He is Director of the Violence Prevention Research Program at the University of California (UC) at Davis. Dr. Wintemute is also Professor of Emergency Medicine at UC.

“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.

"But, since 2006, the gap between the two has been widening, with firearm homicides decreasing and suicides increasing.”

http://www.vocativ.com/usa/guns/suicides-outnumber-homicides-comes-gun-violence/

The doctor's findings have also been confirmed by the New York Times and CBS News.

https://www.nytimes.com/2015/10/09/upshot/gun-deaths-are-mostly-suicides.html

https://www.cbsnews.com/news/guns-used-more-for-suicide-than-murder/