The intelligence menu allows you to view supply and demand of contraband, and track found contraband. it is unlocked by researching Intelligence in the bureaucracy menu (requires a Chief).
There are five tabs available under the Intelligence menu: Danger, 24hrs, 7 days, Informants, and Gangs.
The Danger section shows you all the sources of contraband in your prison (not including items smuggled in on entry or thrown over the walls), how much contraband is in your prison, and how much demand there is for contraband of a particular type.
The 24hrs and 7 days sections show the contraband recovered by your Guards in the specified time frame. Hovering over an item of contraband will show it's path through the prison.
The Informants section is where you can recruit and use Confidential Informants. You may recruit them if they are in Solitary Confinement or, rarely, in Lockdown. Once recruited, they will begin to gather information about the contraband in your prison and the prisoners that have been marked for death (normally Snitches or Ex Law). This information can be viewed by Activating them with a proper Security room available, the informant will be escorted there where they will show you what they know. Searching cells/prisoners that have been marked as having contraband in them will raise your informant's Suspicion level next to their name, if it gets too high they will be marked for death.
The Gangs section is where you can view the different Gangs present in your prison, along with their membership, number of gang-associated kills, and money extorted from an occupied Yard/Common Room. Gang members will show up in the colour of their gang, as well as their cells and any territory they have acquired. If you station enough guards in a Yard/Common Room, they will turn white.