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First Degree Murder Defenses

A charge of first degree murder is not without defenses. A defendant can argue that they didn't commit the killing in question and the police simply have the wrong person. The defendant can also argue that they committed the killing, but they were justified in doing so because of circumstance or a legal justification. Finally, a defendant can argue that they are not guilty of first degree murder because one or more of the specific elements of the crime was not met.

This article discusses the possible defenses to first degree murder. Some of these may be a complete defense, while others may result in a lesser charge of second degree murder or manslaughter.

First Degree Murder Defenses: Mistaken Identity

In first degree murder cases, as well as other homicide crimes, defendants often argue mistaken identity -- that the prosecution has charged the wrong person with the killing. A defendant arguing mistaken identity often asserts an alibi if possible, which he or she tries to support with evidence of being somewhere else at the time of the killing.

Other arguments in a mistaken identity defense include challenges to evidence placing the defendant at the scene of the crime. This can include challenges to witness identification as well as challenges to forensic evidence. A mistaken identity defense may also point to evidence implicating another possible suspect, but courts do not require defendants to do so.

First Degree Murder Defenses: Failure to Prove the Elements

First degree murder is a very specific crime with specific elements, each of which must be proven beyond a reasonable doubt. There are variations in state laws, but generally first degree murder requires:

  • the killing of another person;
  • specific intent to do so;
  • deliberation; and
  • premeditation.

If one of these elements is missing, the crime doesn't constitute first degree murder, although it could still satisfy the elements for second degree murder or even manslaughter. It's the prosecutors burden to prove each one of these elements to a jury. While a defendant's defense may argue that one or more of these elements were not met, the defendant isn't required to do so given the prosecution's burden.

First Degree Murder Defenses: Accidental Killing

Killings committed by accident generally don't constitute murder. Some of these killings may result in liability for voluntary or involuntary manslaughter. However, if the accidental homicide takes place during the commission of a crime or as a result of other criminal intentions, it could be considered first degree or second degree murder. In certain cases, such as parental discipline of children which can result in accidental death, the use of physical force beyond accepted norms can push the killing into murder and, depending on state law, first degree murder.

First Degree Murder Defenses: Justification

There are a number of ways that a defendant can argue that the killing of another person was justified and therefore should not be considered first degree murder.


Not all homicides are crimes, let alone first degree murders. The most common justified homicide is killing is in self-defense. To succeed, a defendant arguing self defense must show that the killing resulted from a reasonable use of force to resist a reasonable fear of death or bodily harm. The defendant cannot have instigated the threatening situation. The degree of force used in self-defense must be proportional to the threat perceived, and the threat perceived must be something that would place a reasonable person in fear of death or great bodily harm. Mere words or insults do not suffice.

The defendant's reaction to the threat cannot take place after the threat of death or bodily harm has passed. Many states require that the defendant attempt to retreat or avoid danger if possible before resorting to the use of deadly force.

For example, if someone incapacitates a mugger with pepper spray, he or she may need to attempt to flee to safety instead of taking out a pistol and shooting the mugger. States differ in the degree to which they require an attempt to retreat if the threat they face occurs in the defender's home.

Defense of Others

The reasonable and proportional defense of others may also be justifiable homicide. You may use force to defend another person from harm if you reasonably believe that intervention is justified and that the person being aided could have had a legitimate claim for self-defense. The same requirements as self-defense typically apply: the use of force must be timely and proportional to the threat faced, and the perceived threat of death or bodily harm must be reasonable.

Exercise of Duty

Certain killings by law enforcement and other public officers qualify as justified homicides. If an officer kills someone in the exercise of duty and without an unlawful intent, recklessness or negligence, that killing generally does not constitute murder, let alone first degree murder. State laws, like California, seek to protect public officers and those acting under their command when a killing results from an officer exercising their legal duty as long as excessive force is not used.

First Degree Murder Defenses: Insanity

Most states recognize an insanity defense to charges of first degree murder. Even states which allow the defense, however, treat it differently and often apply different tests. Most states define insanity, for purposes of determining criminal liability, as cognitively being unable to appreciate the quality of the act being committed, or unable to realize that the act is wrong. Some states also recognize a volitional aspect to "insanity" giving some defendants with disorders affecting impulse control access to the insanity defense.

Get Legal Help with Your First Degree Murder Defense

One of the most serious crimes a person can be accused of is first degree murder. The stakes are high and the penalties can include life imprisonment or worse. Now is the time to have the best possible legal defense. Contact a local criminal defense attorney to discuss your case and learn more about how to defend against a first degree murder charge.

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