Luigi Mangione

Luigi does not deny that he killed Thompson. He doesn’t do it in letters. He doesn’t do it when filmed by press. He doesn’t plead innocence in court.
If Luigi pleads not guilty but doesn't deny killing Thompson, I only see two possible defences: 1. Insanity. 2. Vigilante justice.

Vigilante justice would never pass (unless some of the jurors secretly believe in it and decide to try and acquit him). As for insanity of any kind, it'd have to be extensively demonstrated. Lack of true remorse may make it harder to sell an insanity defence.

The only other defence in that case would be that he was somehow coerced into committing that act, but that defence would also be extremely hard to prove, esp. since the suspect would have had plenty of time to get away from those coercing him and obtain help and protection.

Same thing for new assassination suspect Tyler Robinson.
 
If Luigi pleads not guilty but doesn't deny killing Thompson, I only see two possible defences: 1. Insanity. 2. Vigilante justice.

Vigilante justice would never pass (unless some of the jurors secretly believe in it and decide to try and acquit him). As for insanity of any kind, it'd have to be extensively demonstrated. Lack of true remorse may make it harder to sell an insanity defence.

The only other defence in that case would be that he was somehow coerced into committing that act, but that defence would also be extremely hard to prove, esp. since the suspect would have had plenty of time to get away from those coercing him and obtain help and protection.

Same thing for new assassination suspect Tyler Robinson.
He doesn't have to deny doing it. That's what pleading not guilty is for. If he pleads not guilty, the prosecution's job is to prove beyond reasonable doubt that he did it. All the defense has to do is introduce doubt, or which there is plenty.