Instructions
Get close to the SWAT leader as soon as the battle begins, then press the "A" button to find some cover near him.
Press the "Right Trigger" button without aiming to fire blind shots. The SWAT leader will hear these shots and focus on your current position.
Move to the other side of your cover and use the right control stick to aim at the SWAT leader. Press the "Right Trigger" button to shoot him. These shots will connect since the SWAT leader is focused on where you were, not where you are.
Repeat this process until the SWAT leader is defeated.