The Trap, by Victor Ostrovsky

When beginning surveillance on a new target, you must first make a positive, close-range identification. If all you have is a file photo to work with, how can you get close without arousing suspicion? The case officer will identify a narrow street near where the target lives or works. He'll then create human roadblocks (using agency employees) to force all foot traffic to pass single file. With control of the street, The Trap has been set. When the target is spotted, others will confirm his identity, and from that point on the target will be kept in sight.