The Crimes Code defines Homicide as:

• (a)  Offense defined.–A person is guilty of criminal homicide if he intentionally, knowingly, recklessly or negligently causes the death of another human being.
• (b)  Classification.–Criminal homicide shall be classified as murder, voluntary manslaughter, or involuntary manslaughter.

Murder is defined as:

• (a)  Murder of the first degree.–A criminal homicide constitutes murder of the first degree when it is committed by an intentional killing.
• (b)  Murder of the second degree.–A criminal homicide constitutes murder of the second degree when it is committed while defendant was engaged as a principal or an accomplice in the perpetration of a felony.
• (c)  Murder of the third degree.–All other kinds of murder shall be murder of the third degree. Murder of the third degree is a felony of the first degree.
• (d)  Definitions.–As used in this section the following words and phrases shall have the meanings given to them in this subsection:
  • Fireman.  Includes any employee or member of a municipal fire department or volunteer fire company.
  • Hijacking.  Any unlawful or unauthorized seizure or exercise of control, by force or violence or threat of force or violence.
  • Intentional killing.  Killing by means of poison, or by lying in wait, or by any other kind of willful, deliberate and premeditated killing.
  • Perpetration of a felony.  The act of the defendant in engaging in or being an accomplice in the commission of, or an attempt to commit, or flight after committing, or attempting to commit robbery, rape, or deviate sexual intercourse by force or threat of force, arson, burglary or kidnapping.
  • Principal.  A person who is the actor or perpetrator of the crime.

Voluntary Manslaughter is defined as:

• (a)  General rule.–A person who kills an individual without lawful justification commits voluntary manslaughter if at the time of the killing he is acting under a sudden and intense passion resulting from serious provocation by:
  • (1)  the individual killed; or
  • (2)  another whom the actor endeavors to kill, but he negligently or accidentally causes the death of the individual killed.
  • (b)  Unreasonable belief killing justifiable.–A person who intentionally or knowingly kills an individual commits voluntary manslaughter if at the time of the killing he believes the circumstances to be such that, if they existed, would justify the killing under Chapter 5 of this title (relating to general principles of justification), but his belief is unreasonable.
  • (c)  Grading.–Voluntary manslaughter is a felony of the first degree.

Involuntary Manslaughter is defines as:

• (a)  General rule.–A person is guilty of involuntary manslaughter when as a direct result of the doing of an unlawful act in a reckless or grossly negligent manner, or the doing of a lawful act in a reckless or grossly negligent manner, he causes the death of another person.
• (b)  Grading.–Involuntary manslaughter is a misdemeanor of the first degree. Where the victim is under 12 years of age and is in the care, custody or control of the person who caused the death, involuntary manslaughter is a felony of the second degree.

Self Protection, or Self Defense is defined as:

• (a)  Use of force justifiable for protection of the person.–The use of force upon or toward another person is justifiable when the actor believes that such force is immediately necessary for the purpose of protecting himself against the use of unlawful force by such other person on the present occasion.
• (b)  Limitations on justifying necessity for use of force.–
  • (1)  The use of force is not justifiable under this section:
    • (i)  to resist an arrest which the actor knows is being made by a peace officer, although the arrest is unlawful; or
    • (ii)  to resist force used by the occupier or possessor of property or by another person on his behalf, where the actor knows that the person using the force is doing so under a claim of right to protect the property, except that this limitation shall not apply if:
      • (A)  the actor is a public officer acting in the performance of his duties or a person lawfully assisting him therein or a person making or assisting in a lawful arrest;
      • (B)  the actor has been unlawfully dispossessed of the property and is making a reentry or recaption justified by section 507 of this title (relating to use of force for the protection of property); or
      • (C)  the actor believes that such force is necessary to protect himself against death or serious bodily injury.
  • (2)  The use of deadly force is not justifiable under this section unless the actor believes that such force is necessary to protect himself against death, serious bodily injury, kidnapping or sexual intercourse compelled by force or threat; nor is it justifiable if:
    • (i)  the actor, with the intent of causing death or serious bodily injury, provoked the use of force against himself in the same encounter; or
    • (ii)  the actor knows that he can avoid the necessity of using such force with complete safety by retreating, except the actor is not obliged to retreat from his dwelling or place of work, unless he was the initial aggressor or is assailed in his place of work by another person whose place of work the actor knows it to be.
  • (2.1)  Except as otherwise provided in paragraph (2.2), an actor is presumed to have a reasonable belief that deadly force is immediately necessary to protect himself against death, serious bodily injury, kidnapping or sexual intercourse compelled by force or threat if both of the following conditions exist:
    • (i)  The person against whom the force is used is in the process of unlawfully and forcefully entering, or has unlawfully and forcefully entered and is present within, a dwelling, residence or occupied vehicle; or the person against whom the force is used is or is attempting to unlawfully and forcefully remove another against that others will from the dwelling, residence or occupied vehicle.
    • (ii)  The actor knows or has reason to believe that the unlawful and forceful entry or act is occurring or has occurred.
  • (2.2)  The presumption set forth in paragraph (2.1) does not apply if:
    • (i)  the person against whom the force is used has the right to be in or is a lawful resident of the dwelling, residence or vehicle, such as an owner or lessee;
    • (ii)  the person sought to be removed is a child or grandchild or is otherwise in the lawful custody or under the lawful guardianship of the person against whom the protective force is used;
    • (iii)  the actor is engaged in a criminal activity or is using the dwelling, residence or occupied vehicle to further a criminal activity; or
    • (iv)  the person against whom the force is used is a peace officer acting in the performance of his official duties and the actor using force knew or reasonably should have known that the person was a peace officer.
  • (2.3)  An actor who is not engaged in a criminal activity, who is not in illegal possession of a firearm and who is attacked in any place where the actor would have a duty to retreat under paragraph (2)(ii) has no duty to retreat and has the right to stand his ground and use force, including deadly force, if:
    • (i)  the actor has a right to be in the place where he was attacked;
    • (ii)  the actor believes it is immediately necessary to do so to protect himself against death, serious bodily injury, kidnapping or sexual intercourse by force or threat; and
    • (iii)  the person against whom the force is used displays or otherwise uses:
      • (A)  a firearm or replica of a firearm as defined in 42 Pa.C.S. 9712 (relating to sentences for offenses committed with firearms); or
      • (B)  any other weapon readily or apparently capable of lethal use.
  • (2.4)  The exception to the duty to retreat set forth  under paragraph (2.3) does not apply if the person against whom the force is used is a peace officer acting in the performance of his official duties and the actor using force knew or reasonably should have known that the person was a peace officer.
  • (2.5)  Unless one of the exceptions under paragraph (2.2) applies, a person who unlawfully and by force enters or attempts to enter an actors dwelling, residence or occupied vehicle or removes or attempts to remove another against that others will from the actors dwelling, residence or occupied vehicle is presumed to be doing so with the intent to commit:
    • (i)  an act resulting in death or serious bodily injury; or
    • (ii)  kidnapping or sexual intercourse by force or threat.
  • (2.6)  A public officer justified in using force in the performance of his duties or a person justified in using force in his assistance or a person justified in using force in making an arrest or preventing an escape is not obliged to desist from efforts to perform such duty, effect such arrest or prevent such escape because of resistance or threatened resistance by or on behalf of the person against whom such action is directed.
  • (3)  Except as otherwise required by this subsection, a person employing protective force may estimate the necessity thereof under the circumstances as he believes them to be when the force is used, without retreating, surrendering possession, doing any other act which he has no legal duty to do or abstaining from any lawful action.
    • (c)  Use of confinement as protective force.–The justification afforded by this section extends to the use of confinement as protective force only if the actor takes all reasonable measures to terminate the confinement as soon as he knows that he safely can, unless the person confined has been arrested on a charge of crime.
    • (d)  Definition.–As used in this section, the term criminal activity means conduct which is a misdemeanor or felony, is not justifiable under this chapter and is related to the confrontation between an actor and the person against whom force is used.

Use of force for the protection of others is defined as:

• (a)  General rule.–The use of force upon or toward the person of another is justifiable to protect a third person when:
  • (1)  the actor would be justified under section 505 (relating to use of force in self-protection) in using such force to protect himself against the injury he believes to be threatened to the person whom he seeks to protect;
  • (2)  under the circumstances as the actor believes them to be, the person whom he seeks to protect would be justified in using such protective force; and
  • (3)  the actor believes that his intervention is necessary for the protection of such other person.
• (b)  Exception.–Notwithstanding subsection (a), the actor is not obliged to retreat to any greater extent than the person whom he seeks to protect.

Use of force for the protection of other persons is defined as:

• (a)  General rule.–The use of force upon or toward the person of another is justifiable to protect a third person when:
  • (1)  the actor would be justified under section 505 (relating to use of force in self-protection) in using such force to protect himself against the injury he believes to be threatened to the person whom he seeks to protect;
  • (2)  under the circumstances as the actor believes them to be, the person whom he seeks to protect would be justified in using such protective force; and
  • (3)  the actor believes that his intervention is necessary for the protection of such other person.
• (b)  Exception.–Notwithstanding subsection (a), the actor is not obliged to retreat to any greater extent than the person whom he seeks to protect.

Insanity is defined as:

• (a)  General rule.–The mental soundness of an actor engaged in conduct charged to constitute an offense shall only be a defense to the charged offense when the actor proves by a preponderance of evidence that the actor was legally insane at the time of the commission of the offense.
• (b)  Definition.–For purposes of this section, the phrase legally insane means that, at the time of the commission of the offense, the actor was laboring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing or, if the actor did know the quality of the act, that he did not know that what he was doing was wrong.