. >> investigator demus hernandez will send an undercover officer to do two separate buys at the house he and another conduct surveillance. we rode along with one of the officers to watch the target location on a busy thursday night. >> all right, we're at 118th >> i'll have a good eye on it, i'm not even a block away. so there's quite a few people out on the block, though. they're out on porches, and it's not as quiet as we thought it would be. >> a steady stream of customers arrives within minutes. arrives within minutes. >> we got a van, a minivan that pulled up, we got another cadillac pulling up behind that car. so stand by. all right. somebody in a red jacket just came out of the target house. someone else is coming out. we have a lot of people coming in and out. oh. you got a -- >> all right. i got a car that just pulled in front of me, occupied with two males, they're just sitting in the car right in front of me. looking the same way we're looking. i don't know why and they're on the cell phone right now. >> gangs often employ their own countersurveillance to watch for cops nea