I've been reading Maimonides and came across two things that I found interesting.
Suppose you kill someone who is dying of a lethal disease. Maimonides concludes that that isn't really murder, since he would have died anyway—while pointing out that you have to be really sure he was dying of a lethal disease.
Now suppose someone who is dying of a lethal disease kills someone else. If, being a helpful sort, he commits the crime in the presence of the court, he has committed murder and can be convicted of doing so. If, however, he only commits the murder in the presence of witnesses, there is a problem.
Witnesses, in this case or others, might lie. In other cases, one thing discouraging them from perjury is that if it is discovered that their false testimony led to the execution of an innocent defendant, they will be found guilty of murder and themselves executed. But if their testimony leads to the execution of an innocent defendant who is himself dying of a lethal disease, they won't be executed, because killing someone who is dying of a lethal disease isn't murder.
Since the witnesses are not at risk of execution for perjury, they might commit it, so their testimony can not be trusted—cannot be taken as sufficient evidence to convict someone of murder. So if someone who is himself dying of a lethal disease commits murder, and doesn't do it in the presence of the court, he cannot be convicted.
There is a certain beautiful logic to this very screwy result.
In Maimonides' discussion of what we would call tort law, he considers a number of borderline cases—cases where it is not clear whether the tortfeasor owes the victim a damage payment equal to half the damage or a quarter of the damage done. His conclusion in such cases is that the court can only award the plaintiff quarter damages. If, however, the plaintiff has seized property of the defendant amounting to half damages, the court will not make him give it back.
Part of what is going on here seems to be a rule holding that the court will not transfer property unless it has good reason to do so. It can't award half damages, because it isn't sure that more than quarter damages are owed. But it can't make the plaintiff who has acted on his own to collect half damages give part of the money back, because it isn't sure that half damages aren't owed.
A different way of looking at this is that it represents a hybrid of a conventional legal system, with action by the state or analogous authorities, and a feud system, in which parties act on their own, within some set or explicit or implicit rules, to enforce their rights. I get the same impression looking at the legal rules applied to killing. Under some circumstances, a killer cannot be convicted and punished by the court. But the "avenger of blood," the kinsman of the victim who, in a feud system, would be expected to avenge the killing, can kill the killer with impunity. His right to do so is complicated by various rules, in particular the existence of cities of refuge; once the killer gets to one of those he is in theory safe.
I should probably add that Maimonides is writing at a time when there are no cities of refuge and have been none for a thousand years or so. Substantial parts of his legal code describe what the rules were back when the kingdom of Israel was a going concern and the Temple still standing. One possible explanation is that he believed that that situation was going to be reestablished in the not too distant future—so legal scholars ought to be prepared.