Carol is a police officer and has just come off of a double-shift and is exhausted.She enters her apartment building and climbs the stairs.In her fatigued stated, she climbs the incorrect number of flights of stairs and walks to the door of what she believes is her apartment.The door is ajar.Carol enters the apartment and encounters a strange male in the living room who yells at her.Believing the man to be an intruder, she fires her weapon and fatally shoots the man.It is then discovered that she is in the wrong apartment and the man was yelling at her because she was an intruder in his home.Carol is arrested and charged with murder.

What defense might Carol use to show she did not have the requisitemens reato commit murder?

What ismens rea?