There are several requirements for homicide cases because when a case is taken to court, for defense or accusation, the jury must rule a decision beyond reasonable doubt. For this reason, when a case is built it has to be very solid, and the accusations must answer every question possible. Hence, a protocol is often followed quite thoroughly.
One of the key elements of this protocol is identifying causation: What was the conduit that made the event to take place? Within this definition one asks: Is there a pattern of action that can be established to decide whether the causation was planned, or accidental? That would determine the charges that will be presented in court.
The requirement of "causation" means that a person who is being tried for homicide must be shown to have caused the victim of the crime to die. This sounds like a pretty obvious thing, but it is not always so simple.
In many cases, the causation is obvious. The defendant shot the victim with a gun and the victim died. Clearly, the defendant caused the death of the victim.
But causation is not always so obvious. Let's say that someone drives drunk and crashes into someone else's car, killing them. This could be a homicide. But what if the person who died was not wearing a seat belt? Which thing killed them? Was it the crash? Or was it the fact that they were not wearing the seat belt because, if they had worn the seat belt, they would have survived?
There are no clear ways to define causation -- to define exactly when someone has caused the death of another. But causation must be found in order to prove a homicide.
Causation means that some overt act or omission on behalf of the accused person was the direct and proximate cause of the decedent's death with no intervening cause. A famous law school illustration is that a man jumps from a building with the intent of committing suicide. As he is falling, another man shoots and kills him while he is still falling. He is dead before he hits the ground. The gun shot was the direct and proximate cause of his death. Although he would have died anyway, he would have lived the short time before he struck bottom. The overt act may be as dramatic as a gunshot, or withholding medication from one who needs it. The old common law rule, no longer in effect, was that death had to occur within a year and a day. That is no longer the case. If the victim lingers for years; but the act or omission of the defendant was the direct and proximate cause of his death; then there is causation.
Causation is simply "cause". The actions of person A caused (or led to) the death of person B. At common law there was a rule called the "year and a day" rule where the acts of person A caused someone injury but did not kill them. If the injured person lived beyond a year and a day and then died it was presumed that the cause of death was from something other than the actions of person A. This has been largely superseded by statute.
Causation is a common principle in the law both criminally and civilly.