The NICS system is linked to several databases managed by the FBI, including the National Crime Information Center, and runs an individual's name through federal and state criminal records.

CNN: Background checks on gun sales: How do they work?

Interviews with roughly three dozen of the defendants' friends, relatives, colleagues and teammates, as well as an examination of athletic records, photos, transcripts and civil and criminal complaints filed in a New York federal court, reveal the depth of the relationship among them and how their bonds were broken by the insider-trading case.

WSJ: They Were Best of Friends, Until the Feds Showed Up