In pari delicto
In pari delicto (potior/melior est conditio possidentis), Latin for "in equal fault (better is the condition of the possessor)", is a legal term used to indicate that two persons or entities are equally at fault, whether the malfeasance in question is a crime or tort.
The phrase is most commonly used by courts when relief is being denied to both parties in a civil action because of wrongdoing by both parties. The phrase means, in essence, that since both parties are equally at fault, the court will not involve itself in resolving one side's claim over the other, and whoever possesses whatever is in dispute may continue to do so in the absence of a superior claim. The doctrine is similar to the defense of unclean hands, both of which are equitable defenses.
Comparative fault (a doctrine of tort law that compares the fault of each party in a lawsuit for a single injury) and contributory negligence (applicable when plaintiffs/claimants have, through their own negligence, contributed to the harm they suffered) are not the same as in pari delicto, though all of these doctrines have related policy rationale underpinnings.
The same principle can be applied when neither party is at fault if they have equal right to the disputed property, in which case the maxim of law becomes in aequali jure (melior est conditio possidentis). Again the court will not involve itself in the dispute without a superior claim being brought before it.