The former sheriff of Los Angeles County agreed to testify about gangs that have allegedly taken root in the nation’s largest sheriff’s department next month—after years of mounting evidence that ...

On Nov. 10, the undercover agent met with Arevalo’s alleged associate, Diaz-Ceballos, who sold a short-barreled rifle, a .45-caliber pistol, four machine-gun conversion devices for AR-style rifles and ...