Luigi Mangione Says His Defense Is Extreme Emotional Disturbance

Luigi Mangione wants to mount a seldom-used defense in his murder trial -- Extreme Emotional Disturbance -- and if the jury buys it, Mangione could become a free man one day.

Mangione appeared in court Wednesday with his lawyers, who informed the judge he will use the defense when he goes on trial for the murder of UnitedHealthcare CEO Brian Thompson.

What's fascinating ... the defense would allow Mangione and his lawyers to effectively put UnitedHealthCare on trial, showing the company's conduct in denying claims was so egregious it upset Mangione to the point of meltdown. As TMZ has extensively reported, Mangione was extremely upset with the way corporate greed controlled the United States.

To prevail, Mangione's lawyers would have to show his emotional reaction was "reasonable" under the circumstances, and it manifested itself in a loss of self-control.

And get this ... Mangione doesn't have to prove the emotional distress beyond a reasonable doubt. If the jury believes it's more likely than not that he suffered extreme emotional disturbance, the defense prevails.

The defense is available in New York and several other states. If it sticks with the jury, he would be found guilty of manslaughter, not murder. First Degree Manslaughter carries a minimum prison sentence of 5 years and the max is 25 years. Luigi is 28, so he could regain his freedom.

The judge has not ruled if the defense will be available. That ruling could be a turning point in the trial.

It's fair to expect prosecutors to object to Mangione's lawyers using the defense. They will almost certainly point to the legislative history behind the law, which is rooted in crimes of passion, not premeditated murder.