A small sample of the definition for Felony Murder from Dean's Law Dictionary.
Felony murder has never been a static, well-defined rule at common law, but throughout its history has been characterized by judicial reinterpretation to limit the harshness of the application of the rule. Some, dead set against the rule, historians and commentators have concluded that the rule is of questionable origin and that the reasons for the rule no longer exist, making it an anachronistic remnant, 'a historic survivor for which there is no logical or practical basis for existence in modern law'. Moreland, Kentucky Homicide Law With Recommendations, 51 Ky L J 59, 82 (1962).
The first formal statement of the doctrine is often said to be Lord Dacres' case, Moore 86; 72 Eng Rep 458 (KB, 1535). See, e.g., Crum, Causal Relations and the Felony-Murder Rule, 1952 Wash U L Quarterly 191; Morris, The Felon's Responsibility for the Lethal Acts of Others, 105 U of Pa L Rev 50, 58 (1956). Note, Recent Extensions of Felony Murder Rule, 31 Ind L J 534, fn 3 (1956). Lord Dacres and some companions agreed to enter a park without permission to hunt, an unlawful act, and to kill anyone who might resist them. 'Le Seignor Dacres & auters accord de enter en un pke & de hunter la, & de tuer touts que eux resisteront: & accordant al ceo ils entront en le Park, & un vient al un de eux, Et demand, que il avoit de faire la; & l'auter luy occide, le seignor esteant un quarter dun mile de cest leiu, & rien scavoit de ceo: uncore ceo fuit adjudge murder en luy, & en touts ses companions. Et auxi un auter vient en un Orchard, pur gatherer pears & un a luy vient & rebuke luy, & il luy tua, le quel fuit adjudge murder.' While Lord Dacres was a quarter of a mile away, one member of his group killed a gamekeeper who confronted him in the park. Although Lord Dacres was not present when the killing occurred, he, along with the rest of his companions, was convicted of murder and was hanged. Contrary to the construction placed on this case by those who see it as a source of the felony-murder rule, the holding was not that Lord Dacres and his companions were guilty of murder because they had joined in an unlawful hunt in the course of which a person was killed, but rather that those not present physically at the killing were held liable as principals on the theory of constructive presence. Moreover, because they had agreed previously to kill anyone who might resist them, all the members of the group shared in the mens rea of the crime. Kaye, The Early History of Murder and Manslaughter, Part II, 83 L Quarterly Rev 569, 578-579, 593 (1967); see, also, King v Borthwick, 1 Doug 207, 212; 99 Eng Rep 136, 138-139 (KB, 1779).
Thus, because Lord Dacres' case involved express malice, no doctrine finding malice from the intention to commit an unlawful act was necessary or in fact utilized. Note, Felony Murder as a First Degree Offense: An Anachronism Retained, 66 Yale L J 427, 430, fn 23 (1957) (hereinafter cited as Anachronism Retained); Recent Developments, Criminal Law: Felony-Murder Rule -- Felon's Responsibility for Death of Accomplice, 65 Colum L Rev 1496, fn 2 (1965) (hereinafter cited as Felon's Responsibility). .....