In Salinas, guns used in crimes get around
Weapons often pass from shooter to shooter
Monterey Herald : Julia Reynolds : September 10th 2006

Link:
http://www.montereyherald.com/mld/montereyherald/news/15485577.htm

Summary:
This article tracks a CZ 85, Czechoslovakian Pistol, that was used in multiple murders in Monterey County. Salinas police officers attribute the multiple murders to the weapon being traded around. This type of weapon has come to be called a “community” weapon, because it has been used by many people in many crimes. According to ballistics evidence, sometimes guns are even passed between rival gangs. One Norteno, a northern gang that rivals the Surenos, a MS-13 related gang, commented, that once a gun has been used, gang members want to get rid of it. So, sometimes guns are passed or sold to friends, who pass to friends, who then might sell to a rival gang. In response to this problem, the Salinas Police Department has started its own data acquisition station, and hired one of the state's top ballistics experts, Stephen O'Clair, to run their Integrated Ballistics Information System, also called IBIS. This system is now able to link the same gun to different crimes based on ballistics from the bullet and the shell, even if the weapon is never recovered. O’clair has identified and is now tracking 160 weapons, though the police have recovered none of them.

Analysis:
Community guns have become a problem in other areas as well. The high rate of transfer of weapons is not only driven by a perpetrators urge to dispense with a weapon that has been used in a crime. But, also gun sharing. I have read reports of weapons being used by gangs and stored/cached in public areas, so that a search of their residences would not recover anything incriminating.