@clarity Reminds me of a bit of advice that's often given in NSR circles: Tell your players when their characters think they're being lied to.
A lot of times, the GM instinct is to try to make the NPC sound fishy and let the players sort it out for themselves, but that stuff can fly right past even clever players. Just say, "Alcestis tells you she didn't see the murderer's face, but something about her claim seems a bit off."