Huck stops to try to save the murderers because he feels bad for them. He thinks that there is a possibility that he could have been a murderer, and he wouldn't want to be stuck on a wrecked steamboat. This shows that Huck is very capable of empathy towards others. He can see people that are in the worst walks of life and picture himself there, and then conduct himself according to how he would like to be treated. It also shows that Huck has a slightly warped moral judgement. He is willing to do anything to keep himself alive, but when he looks back at things he did that is when he feels bad. It also emphasizes his youth again and his lack of a look before you leap attitude.