I wish I had a video of that or something, I really do...
Wasn't hard to get the kills themselves, the 2 riflemen were perched over the ledge, completely oblivious to me having climbed up, even though the collaborators started panicking and jumping around as soon as I got onto the roof.
The RPG guy, however, almost got in a double KO, because he ran up behind me (I didn't even notice him at first, in my haste) and let a round loose in fear, but luckily it vent past my head and into the abyss.
Arresting the civvies wasn't all that easy though, since they continued jumping around like crazy. Got the first one in 3 tries, then the second one tried to revive one of the riflemen but he only opened himself up for an easy arrest. During all that, I saw the third civvie start climbing down the rope, so as soon as I was done I ran over to the grappling hook and pressed G. I looked over the edge and sure enough he was lying on the ground dead.
This all happened Sunday night on the ]H[ Clan's server. Can't remember which map, I'm not familiar with the names yet. The building in question was one of those really tall, what I presume to be a Hotel buildings. Not quite sure how they got the grappling hook all the way up there either. Climbing it took a good 30 seconds, and there were no ladders on this one.