Amber Guyger was convicted of murder: entering the apartment of Bothum Jean and shooting him. She claimed she thought she was in her apartment. How would a defense of "mistake of fact" apply in said case? IANAL and seek to understand the subject matter
Amber Guyger was convicted of murder under Texas Penal Code section 19.02:
A person commits the offense of murder if the person 1) intentionally or knowingly causes the death of an individual or 2) intends to cause serious bodily injury and commits and act clearly dangerous to human life that causes the death of an individual.
The Texas mistake-of-fact defense is codified at Penal Code section 8.02:
It is a defense to prosecution that the actor through mistake formed a reasonable belief about a matter of fact if his mistaken belief negated the kind of culpability required for commission of the offense.
To assert a mistake of fact defense, then, you need to demonstrate that you reasonably believed something that changes whether or not you met the mens rea requirement of intentionally or knowingly causing a death/serious bodily injury.
An example would be firing a gun at what you reasonably thought was a corpse, or a mannequin, or Superman. In any of those circumstances, you would not have intended or known that you were going to cause someone's death. If you reasonably believed your gun was unloaded, you would not have known you were going to kill someone if you pulled the trigger.
In Guyger's case, Whether she was in her apartment or someone else's, she still knew that putting two bullets in a man eating ice cream would cause his death or serious bodily harm.
In the Guyger case, the defendant claimed she was mistaken about what apartment she was in, but that doesn't change whether she had the intent to kill Mr. Jean.
That mistake does implicate the Texas "Castle doctrine" statute, Penal Code section 9.32:
A person is justified in using deadly force against another ... when and to the degree the actor reasonably believes the deadly force is immediately necessary ... to protect the actor against the other's use or attempted use of unlawful deadly force.
The actor's belief ... that the deadly force was immediately necessary ... is presumed to be reasonable if the actor ... knew or had reason to believe that the person against whom the deadly force was used ... unlawfully and with force entered ... the actor's occupied habitation
If her mistake was reasonable, that would give her reason to believe Mr. Jean had unlawfully and with force entered her home, making it presumptively reasonable that she used deadly force.
But the mistake of fact defense only looks at mistakes that change whether you committed the offense, not whether an affirmative defense is available to you, so it doesn't really change whether the defense is available.
Nonetheless, it's generally accepted that a person can use self-defense doctrines like this even when they're mistaken about whether they're in danger. The question for the jury in those cases is whether the defendant's mistake was reasonable.
Because the jury convicted her, it necessarily did not believe that she had made a reasonable mistake.
I am going to answer about the general principles of Mistake of Fact and use as an example a simplified hypothetical case similar to the Amber Guyger case as reported in online news stories. I do not assume that these reports are either complete or fully accurate, so please treat my example only as a hypothetical case where similar principles may apply.
Mistake of Fact as an aspect defense to a criminal charge goes to the element of intent, or Mens Rea (guilty mind). The mistake is not usually a defense in and of itself, but may establish or help to establish tha the accused did not have the required criminal intent.
In many jurisdictions the mistake must be reasonable.
As intent is, in many cases, an element of the crime, once that element has been placed in issue by the accused alleging a Mistake of Fact, the prosecution must prove that element, like all other elements of the crime, beyond a reasonable doubt. If the jury (or judge in a bench trial) has a reasonable doubt about the intent of the accused, there should be an acquittal.
For example, if a person breaks into a house, honestly but mistakenly believing that is is his own house, this will be a defense to a charge of breaking and entering, or trespass.
However, if a person breaks into John's Jewels, thinking that s/he was breaking into Bob's Bakery, the mistake will afford no defense, as the act was a crime even had the accused been correct about the situation. Making a mistake about which crime one was committing is no defense when the accused knew (or should have known) s/he was committing a crime.
Similarly, a person taking another's bag from an unlocked storage area in mistake for his or her own bag will have a defense against a charge of theft, if the mistake was reasonable. But a thief who intended to steal Jane's bag but took Martha's by mistake has no defense based on the mistake, even if Martha's is far more valuable and moves the crime from petty to grand theft.
Strict Liability Crimes
In crimes where strict liability applies, that is, where there is no element of intent, a mistake of fact by the accused will generally not offer any defense.
For example, suppose a person of thirty has sex with a person of sixteen, mistakenly thinking that his or her sexual partner was actually 19. In many jurisdictions this mistake of fact will offer no defense, even if it as reasonable, even if the accused had done some investigation to attempt to verify the age of his or her partner. Statutory Rape has, in many jurisdictions, no element of intent at all, and merely proving that the sex occurred and the actual age of the minor participant is enough for conviction.
There are other offenses which do not include an element of intent.
The basic law of Mistake of fact in a context of a criminal accusation can be found at:
A number of other similar online sources can be found with a simple gogle search.
The Hypothetical Ann Gale Case
Ann Gale entered her apartment building, but by mistake went to the wrong floor. She went to th4 apartment of Bob Jones, which was located just above her own. There were various indications that she was on the wrong floor, but she did not take note of them.
Ann opened the door, and saw Bob sitting in a chair eating a hamburger. The decor was different than the decor of her own apartment, but the did not take note of that. She drew a pistol which she was legally carrying and, without warning or discussion, shot Bob dead. She said afterwards that she believed that she was in her own apartment, that Bob was an intruder, and that she was in danger. She promptly summoned law enforcement, and did not attempt to conceal her actions.
Ann claimed at trial for second degree murder that there was a mistake of fact, and that she acted in self defense, believing herself menaced by an intruder. She claimed that she had no criminal intent.
The prosecution argued that her mistake was not reasonable, because there were multiple indications that Ann wa son the wrong floor which she ignored. The defense presented evidence that a number of other resident had made similar mistakes, claiming that this proved the mistake reasonable.
The prosecution also argued that a reasonable person, even seeing an intruder in that person's apartment, where the intruder did not have a weapon, and was peacefully eating food, would not use deadly force without warning or inquiry, and that anyone doing so exhibited a "depraved indifference to human life" and therefore would be guilty of murder. Therefore, the prosecution argued, the mistake was unimportant, because even if Ann had been correct about what apartment she was in, her actions would still have been criminal, and still showed a criminal intent.
No one suggested that Ann specifically intended to kill Bob, or indeed that she intended to kill anyone before she entered Bob's apartment. The jury convicted based largely on this final prosecution argument.
(I am not sure if these were exactly the arguments used in the real case on which this example is based, nor does it matter for my example. Please take the example as stated.)
Analysis of the Ann Gale Case
Given the evidence as hypothesized, the jury made a reasonable decision. It is at least arguable that the mistake, even if reasonable and honestly made, did not negate her criminal intent. A person who acts unreasonable or unlawfully takes the risk that his or her actions may be more serious than s/he realizes at the time.