I spent an age looking around for them, first by sneaking into the mansion. Saw nothing out of the ordinary there, and had considered going deeper, but felt I'd only do that as a last resort. Managed to sneak back out again to check the back alleyways of the town. As soon as I got there, out they appeared. I followed them around a bit to mark where they'd go, then hit the restart. Even with the knowledge, I never saw many openings, and I couldn't use the explosive duck just in case it hurt the one you're not meant to hit and failed me. Replanned to get my emetic dart gun out, hit the guy, then followed him to the toilets. The guards followed me inside! Rather than restart, I punched them out as best as I could, then got the target. Not exactly clean, but it got the job done.