Am I allowed to kill a person threatening me? CA, USA
<p>You are riding a public transit train and out of nowhere a man with blue jeans takes out a P99 semiautomatic pistol and takes the passengers hostage. Luckily you have a knife on you. But you don't know whether it is legal to kill a person under such circumstances. Hence the question: is it legal to kill the man who is threatening your life, and the lives of countless others? Context is California, USA.</p>

<p>I would just like to clarify, in addition to the other answers and what Dale M alluded to, one important detail: Unless you are carrying out the death penalty, no one under any circumstances is allowed <strong>to kill</strong> anyone else. What you <em>are</em> sometimes authorized to do, is <strong>to use deadly force</strong>. </p>

<p>There is an important distinction between the two. When using deadly force, you are using extreme force to stop someone doing something, which may result in getting that person killed, but killing isn't the point, stopping whatever he is doing is.</p>

<p>If instead of a knife you had a gun on the train, you shot the guy in the face, his crime spree came to and end, yet he was still alive but unconscious, and you decided to "finish the job" and shoot him some more, you'd be going to prison.</p>

<p>The language is important. Even if in self defense situations, if you say that you were shooting to kill, you're going to be in serious trouble, but if you say you were shooting to stop, you're in the clear.</p>

<p>According to <a href="http://www.leginfo.ca.gov/cgi-bin/displaycode?section=pen&amp;group=00001-01000&amp;file=187-199" rel="noreferrer">California Penal Code Section 187</a></p>

<blockquote>
  <ol start="187">
  <li>(a) Murder is the unlawful killing of a human being, or a
  fetus, with malice aforethought.</li>
  </ol>
</blockquote>

<p>Penal Code section 197 and 198:</p>

<blockquote>
  <ol start="197">
  <li><p>Homicide is also justifiable when committed by any person in
  any of the following cases:</p>
  
  <ol>
  <li>When resisting any attempt to murder any person, or to commit a
  felony, or to do some great bodily injury upon any person; or,</li>
  <li>When committed in defense of habitation, property, or person,
  against one who manifestly intends or endeavors, by violence or
  surprise, to commit a felony, or against one who manifestly intends
  and endeavors, in a violent, riotous or tumultuous manner, to enter
  the habitation of another for the purpose of offering violence to any
  person therein; or,</li>
  <li>When committed in the lawful defense of such person, or of a
  wife or husband, parent, child, master, mistress, or servant of such
  person, when there is reasonable ground to apprehend a design to
  commit a felony or to do some great bodily injury, and imminent
  danger of such design being accomplished; but such person, or the
  person in whose behalf the defense was made, if he was the assailant
  or engaged in mutual combat, must really and in good faith have
  endeavored to decline any further struggle before the homicide was
  committed; or,</li>
  <li>When necessarily committed in attempting, by lawful ways and
  means, to apprehend any person for any felony committed, or in
  lawfully suppressing any riot, or in lawfully keeping and preserving
  the peace.</li>
  </ol></li>
  <li><p>A bare fear of the commission of any of the offenses mentioned in subdivisions 2 and 3 of Section 197, to prevent which homicide may
  be lawfully committed, is not sufficient to justify it. But the
  circumstances must be sufficient to excite the fears of a reasonable
  person, and the party killing must have acted under the influence of
  such fears alone.</p></li>
  </ol>
</blockquote>

<p>Defense of others: 197.1 talks about any person - this raises the concept of "defense of others." Generally speaking, one can use force to defend another person if that person could have legally used the same force. In the example you give, the person being held hostage could have used deadly force to defend themselves and, therefore, a third party can use deadly force defending that person.</p>

<p>Here is a video from a defense attorney and former California District Attorney giving a good lesson on California self defense laws: <a href="https://www.youtube.com/watch?list=SPWMyGtcnDIhFQenEJtxhsuQmMLiywbOzM&amp;v=aUBdU2qv5XM][2]" rel="noreferrer">California self-defense laws - A former D.A. explains (YouTube).</a></p>

<p>I'm licensed to teach firearm law in Arizona and Louisiana. We never teach "shoot to kill" or tell people that they can kill someone. The legitimate purpose of self defense, using firearms or any other force, is to stop an imminent attack where the defender reasonably fears for their life or grave bodily injury. If someone happens to die as a result of a person using reasonable force in a self-defense situation then they may, indeed, be charged with murder. It will be a matter for a trier of fact, a jury or a judge, to determine if the use of force was reasonable and if, therefore, the level of force used was justifiable as an affirmative defense against the charge of murder.</p>

<p>If you have a reasonable belief you or someone else is in imminent danger you have the right, under California law, to defend yourself with "no more force than was necessary to stop the threat." 
Which means that yes, in that situation you would be acquitted of murder and assault charges.</p>

<p>However, if the knife falls afoul of local weapon laws, you could find yourself facing weapons charges.</p>

<p>(I am not an attorney so make sure you also consult an attorney for legal advice.)</p>

<p>The doctrine of <a href="https://en.m.wikipedia.org/wiki/Self-defense_(United_States)" rel="noreferrer">self defence</a> makes it legal to use <em>reasonable</em> force to defend yourself and others against the threat of <em>unlawful</em> and  <em>immediate</em> violence.</p>

<p>There is no question there is a threat of violence, there is no question it is unlawful, it would be legal if it could be demonstrated the threat was immediate or that a reasonable person would believe it was <strong>and</strong> the force you used was reasonable also - using force to disarm and restrain the perpetrator is reasonable; continuing to use force after that is not.</p>

california murder self-defense