My character is a Halfing Rogue specializing in lying and ranged sneak kills with a concealed crossbow. With the Childlike and Pass for Human feats plus max ranks in Bluff I'm crazy good at a believable lie if I act like a child and in theory I could eat the impossible bluff check with the -20, but DM discretion means anything close enough to impossible is just a no-no.
This is a problem for me because this situation is fairly common: I'm near a group of humans, totally docile towards me (or at least not attempting to kill me) and I need to kill them. I can sneak attack one by luring them away, maybe even a couple, but eventually I may need to kill someone in sight of their buddies. Practically speaking the -20 penalty on stealth after a snipe is nothing to me, however living targets will naturally assume someone killed their friend, I'm the only suspicious one around...and "lol I dunno how that bolt wound up in his eye" isn't a useful lie.
Is there some way I can spin the situation, either with a clever lie or less obvious murder (the arrow-in-face method is pretty suspicious) which could plausibly reduce the "I didn't kill that guy" lie from impossible to a far-fetched or unlikely lie? I'm not worried about the actual bluff check, by DM rules I will fail an impossible bluff check.
The tactical issue is mostly convincing the DM that the target could believe the lie, so magical items etc. won't really help unless they can build up some plausible deniability. In the game world most enemies are human so Childlike means as long as I sound innocent, I'll pretty much always pass a bluff check unless my cover is blown. Is there some way (non-lethal weapons, specific lies, Rube Goldberg-esque murders) I could kill someone, be the only visible suspect, but still get no worse than a far-fetched bluff check? Assume I haven't actually been seen doing it, but they have seen the body.