Is there a moral difference between killing, and letting die?

In short, yes there is a moral difference between killing and letting die, but not always. But the issue with these kind of moral dilemmas is that there is no single answer, and everything lies in the circumstances of the situation and decisions that are made. I will cite for an example the recent cruise ship wreck off the coast of Italy. The Costa Concordia capsized killing 17 people and the captain is charged with abandoning the ship before all of his passengers were safely evacuated. Some people in Italy want to charge this man with murder! But when you look at the circumstances, you might agree that all this man is guilty of is cowardice and recklessness. Unlike murder, the decisions he made were not based in malicious intent, but rather in self-preservation and fear which is only human, which is just about all we can ask a person to be. But if the situation were different, and the actions that would prevent someone's death were reasonable, letting die brings with it certain guilt. I will cite another situation in New York where a homeless man, Hugo Alfredo Tale-Yax was stabbed multiple times and left in the street to die after saving a woman from the attacker in Queens, New York. A total of twenty-five people walked passed the collapsed and dying man without coming to his aid. After an hour and a half someone finally shook Hugo and he was rushed to the hospital where he was pronounced dead at age 31. In this situation, any one of those passer-by's could've easily called for help on their cell phone or gotten the attention of someone who could. In my opinion, when letting die comes down to a decision such as this and you let someone die, you are almost as bad as the murderer. And another possible scenario for consideration, letting someone die intentionally where you had the direct chance to intervene, but chose not to so that the person would die. For example, you're on a hike in the Amazon and you come across your long time enemy waist deep in quicksand. You have the necessary gear to help them out, but instead you ignore their cries for help and keep walking. In my opinion this murder all the same because the intent to kill was there.