The earliest you can get this is Contract 03. Leave the blood up and corral the three guards around the rocks (as this gets the stationary guard as well as the secondary patrol). If you slide into the blood, you may be able to catch the third before turning right back around and seeking sanctuary in one of the three hiding spots that the level provides. If you don't wish to try with this level, there are plenty of other opportunities further on as the guard count does increase. Furthermore, some levels will even provide an Agent-type, noted for their radio chat and gray suits; if you encounter them, they'll leave the map and spawn two more basic Guard-types.