The evidence against him appears to be that the guy who murdered the CEO might have similar eyebrows to Luigi Mangione, but it's hard to tell from the security video. There's nothing else that puts him at the scene. They can say it's him all they want, but they'll have to reveal some better evidence if they want us to believe it.
If you're going to court for any criminal charge, you plead not guilty. The DA is going to have laid the strongest charges they believe they can get a conviction on, but there is always risk in going to trial. The prosecution generally cares a lot more about getting a conviction than what charge that conviction is on, or what penalty that conviction carries.
So. You're caught dead to rights, charged with a crime. If you plead guilty, you are also waiving your right to trial, and taking whatever conviction and (probably) penalty the prosecution advises the judge.
On the other hand, if you plead not guilty, now you have the opportunity to accept a plea deal from the prosecution - changing your plea to guilty - which would include what charge and what penalty. Depending on what you've done, this can save you a lot of money, reduce or eliminate probation or incarceration time, or take the death penalty off the table.
You can always change your plea from not guilty to guilty. You can't do that the other way around. Whenever you see headlines about "So-and-so pleads not guilty," that doesn't (in most cases) mean they intend to beat the charge. It's just what you do.
Another huge, important, but subtle distinction to make here is that the trial is not to decide whether you did the thing. It's not always a mystery who perpetrated an alleged crime. Even if you pull out a gun and shoot somebody on the 50-yard-line at the Super Bowl, and 300 million people see it, they can't just take you off to prison for murder. They have to give you a trial to determine whether you violated the law.
There's a thing called an affirmative defense, as in, "yes, I did the thing, but it wasn't a crime, because..." If you can, say, convince a jury that you're a time traveler, the ref was going to make a bad call in the 4th quarter that cost your team the Super Bowl win, and that justified shooting him, well, then it wasn't a crime. That's what a jury is ultimately charged with deciding.
This is not to say that Magione's attorney plans to present an affirmative defense, just that there are a number of good reasons to plead not guilty, even if it's 100% certain you did the thing.
Judicial system working like this (including the previous comments about pleas) is something I would've probably doubted if I read it in a fiction, but here we are
Guilty or not, always plead not guilty at the start. You'll often have a chance to accept a better plea deal before trial if you want. Or you can go to trial.
Unless you are looking forward to serving time (free food, warm bed, access to healthcare).
If you are picked for a jury, I know it can be annoying and take time out of your busy life. But honestly, it is the last purely democratic area of our life. The jury has the power to ensure the laws are fairly and equally applied.
Remember that your job as jury is to not only find the facts of the case but also to make sure that the charges fit the crime.
There is one more job you have: is the law correct in this specific crime?
Judges won't tell you this. Prosecutors will make you leave this choice outside the courthouse. But you have it.
The responsibility of the jury is protected so that you cannot be held accountable or even questioned (in an official setting anyway) as to why you voted the way you did. You have the power to view the facts, know that the defendant is guilty, but vote to acquit because you believe the law is wrong in his case.
Yeah, the absurd terrorism charges are probably possible to beat, so no reason to plead guilty to them. They are probably not questioning the murder charges, but that's beside the point.