There is a natural duty not to murder, but there is also another natural duty to rescue people from life-threatening situations, especially if getting into one is not the person's fault, and if you are in a position to execute the rescue successfully.
I am not saying that the government can punish a person for failing to rescue anyone, so it is a moral not legal duty.
There could be many other caveats here, but let's agree that in appropriate circumstances, there is a natural duty to rescue.
Long story short, dilemma #1. You own ten hearts that can save the lives of 10 patients needing heart transplants. However, if you withhold the hearts, these patients will die, and their kidneys will be used to save the lives of 20 patients needing kidney transplants. Assume no other hearts of kidneys are available. What do you do?
Dilemma #2. An evil colonel has 20 prisoners. He has arranged them in two sets of 10 in front of you and says: "If you personally right now take this gun and kill every person in one set, then the other set, i.e., the other ten prisoners, will go free. If you refuse to kill, then I'll personally and right now kill all 20 of them." Again, what do you do?
Imagine that the prisoners are women and children, to make the problem more heartbreaking.
This is similar to the dilemma posed in the movie Dark Knight. Two ships are immobilized at sea. Bombs are planted in each one. The people in ship 1 are given a remote control activating which will destroy ship 2, and vice versa for the people in ship 2. Joker stipulated additionally that if both ships are alive after 12:00 hits, then both ships will be destroyed; otherwise the surviving ship is spared.
Notice that these are not utilitarian dilemmas, because in both cases we are dealing with survival which is prior to pleasure. You can't get any utility when you're dead. If one survives, then no further actions are specified; this person will go and live his life and indeed, seek future happiness however he sees fit. Whether he goes to heaven or whether it would have been better if he had died during the resolution of the dilemma is his own business.
These are, however, consequentialist dilemmas, insofar as we have two natural duties (not to kill; to rescue) in serious conflict with no apparent way to decide which duty prevails on absolutist grounds, yet picking one yields better consequences (again, in terms of lives saved though not happiness imparted) than the other.
Thus, for the evil colonel problem, killing 10 men will make you a murderer, but you save 10 lives. Refusing to kill means that you wash your hands of the whole affair, but you have to live with the thought that, had you done otherwise, 10 lives would have been spared. Similarly, better consequences will result if any one ship destroys the other; but that'd again make the people in the first ship murderers. Neither is a pretty choice.
Be sure to play with the numbers to test your answers; for example, what if the colonel had 2 million prisoners? Would you still not kill the 10?