order up guy. you call him up, let him know what you want. nothing less than a 20. >> it's in the middle of a nonstop week for the cook county sheriff's south gang unit based in chicago's south suburbs. investigator matt jenna is juggling five cases at once and has many more in the pipeline. >> we've arrested this guy seven times out of this apartment alone, seven times. ten arrests in his background. >> on average, the sheriff's gang units serve ten search warrants for drugs and guns every month. jenna and his colleagues are focused on places like robbins, harvey, and mid lothian. in fact, the south suburbs represent the single hottest focal point of gang activity outside of chicago city limits. >> there is gunfire, have a position to cover that you can move to. >> all right, guys. let's gear up. go outside and rehearse. >> going to go and hit it and grab this guy. that guy sells a lot of crack