The bandits killed in a fairly secluded area so it is not like that many people would even have an idea of what they did.  Also it is not like bandit groups just stick to a single hideout most of the time and often move around while staying at least close enough to good 'hunting grounds'.  Also you have to consider Crosshaven is not exactly a town of any great importance, unless tax routes are being threatened whoever rules the area probably won't send any troops to the area, which makes merchants have to hire protection and such.  Also such a group would know the land quite well and therefore be able to avoid detection most of the time.