Also, approach other officers for information. Your local custody officers can help you locate local O.G. or "Veterano" gang members willing to talk about tattoos, hand signs, graffiti, and gang histories. Interview them and record these sessions.
Whatever you do, be sure to commit these gang histories to writing. We failed to do this in the beginning years of LASD gang unit Operation Safe Streets and regretted it later. The information was readily available then, so we didn't think we needed to record it. But after a lot of those O.G.s died, we no longer had sources for that information and we had no records of our interviews. This is how history was revised to make Stanley "Tookie" Williams the "heroic co-founder" of the Crips.
For some reason, many gang members find it easier to speak about "La Vida Loca" while in custody. A cup of coffee, a phone call, or a cigarette, used to work wonders. Today you could probably get fired for giving an inmate a cigarette, but look for other perks you can use. But remember, never take the word of one jail house informant as gospel. Corroborate his or her story when you come in contact with other members of that same gang.
A gang is a separate culture. No matter how street wise you think you are, you'll need to study that culture in order to communicate with its members. Learn their slang terms, read their magazines, and listen to their music. The more that you know about their culture, the more freely they will talk about confidential gang matters. A word of caution on this: Know their slang and culture, but don't talk like them or imitate their mannerisms. You are not a gang member.
Informants, Contacts, and Colleagues