Pari delicto – this legal phrase comes from Latin and it is used for “of equal fault.” For example, if two parties complain to a judge about non-performance of a contract by the other, the judge could refuse to decide for compensation to either of them because of  the “pari delicto” rule: the court finding that they were equally at fault in causing the contract’s breach so they don’t deserve compensation due to their wrongfully behavior.

See also http://dictionary.law.com/Default.aspx?selected=971 .