I don't think they may have been the ones to kill him. They could have put trust in him, sent him a note to meet and he saw Higekiri doing something shady? It's hard to say, I didn't know either of them very well before they died.

Unless the Madame and Bartender are like the Deputy where their role can double as both good and bad. Or they were working with the Bandits that week, saw Manfred as a threat and helped set the stage so Higekiri and the other Bandit could kill him. The problem is that this opens up way too many possibilities now.