Use the building just to the right of the Boyle Estate during the "Lady Boyle's Last Party" mission. Evade the Tallboy that patrols outside the manor, and eliminate the single footman patrolling the path in front of the building. Go inside the lit archway, and move around the corner to find six Weepers. The game will auto-save here. Use Bend Time 2 then use the crossbow to head shot them quickly.