Today, the mental element of the crime of murder has expanded and developed. In addition to intent, negligence in the use of thought and reasoning—despite the capability of foreseeing a harmful result—is also included. Fault, in its narrow and specific sense, constitutes the mental element of unintentional crimes. However, fault in its general sense refers to a situation where the perpetrator lacks intent and deliberation; therefore, whenever the offender is devoid of intent, he is still considered at fault.

The concept of fault in its broader sense has been taken into consideration in determining the various types of homicide under the Islamic Penal Code (2013) of Iran. In some cases, this broader understanding of fault has led the act of killing to depart from its original nature and assume a new legal character.

The greatest impact of fault is observed in pure accidental homicide, which has been given three legal forms. If it involves simple negligence, it is regarded as quasi-intentional homicide according to paragraph (c) of Article 291 of the Islamic Penal Code. If it falls under the exceptional provision of Article 292 (conscious recklessness), it is deemed intentional homicide. In other cases, it remains subject to the inherent rules of pure accident.

In England, fault in homicide has recognized degrees, each bearing distinct legal consequences in practice. Thus, manslaughter (non-intentional homicide) is divided into manslaughter with simple negligence and manslaughter with aggravated negligence. In aggravated negligence, the actor demonstrates a high degree of lack of foresight, which—both ordinarily and logically—deserves a harsher criminal penalty compared to someone who acts with mere simple negligence.