A study made by the Pittsburgh Graduate School of Public Health reveals that 80% of all gun crimes are committed using illegal guns and the 20% that are legal were obtained before the user had a criminal record.

From Breitbart News:

The Washington Post published the study, which looked at guns recovered from Pittsburgh crime scenes in 2008 and found that “in approximately 8 out of 10 cases, the perpetrator was not a lawful gun owner but rather in illegal possession of a weapon that belonged to someone else.”

Roughly one out of five guns, 18 percent, were used in crimes by the people who actually purchased them. This latter group would consist of people with criminal intent but no criminal record to prevent them from passing a background check. Such people have legally acquired weapons, then killed innocents at Virginia Tech University (2007), Fort Hood (2009), Aurora movie theater (2012), DC Navy Yard (2013), Fort Hood (2014), Chattanooga (20105), Umpqua Community College (2015), Orlando (2016), among others.

In August 2015, the University of Chicago Crime Lab released a similar study that looked at criminal acquisition of firearms in Chicago. As with the Pittsburgh study, researchers found that criminals in Chicago get their guns in ways that are hardest to detect. According to the Chicago Sun Times, crime lab co-director Harold Pollack said, “Some of the pathways [regarding guns] people are concerned about don’t seem so dominant.” He also said very few individuals jailed on gun charges indicated using gun shows or the Internet to acquire firearms. Rather, they get the guns in undetectable ways on the street. Pollack added that the inmates know they run the risk of being caught by police but “were less concerned about getting caught by the cops than being put in the position of not having a gun to defend themselves and then getting shot.”

Many gangs keep one member with a clean record who can then purchase guns for the gangs.