You're 100% right, and that's not even gaslighting. That's exactly the question everyone SHOULD be asking.
Do we know he did it? Absolutely not. And unless a jury reaches a guilty verdict, we are all supposed to assume he did not do it. That's exactly how the presumption of innocence works.
Everyone saying that we all know he did it is just doing the prosecution's job for them. We don't know that Luigi Mangione is the guy in the CCTV footage. The prosecution has to prove that he is, and if they can't, he gets acquitted.
And that's exactly why the media has to say "alleged". It wouldn't even matter if they had footage that clearly showed his face, because the media and the general public doesn't get to decide if someone is guilty or not.
And that's why it's so good that his lawyer has already called this out, because without the presumption of innocence, you can't have a fair trial.
In every court case, the burden of proof only falls on one side, and in criminal cases, it's always on the prosecution. So basically that means if you are on trial, you walk into a court where the assumption is that you are not guilty, and the prosecution has to convince the jury that you are guilty, while the defense just has to raise reasonable doubt.
Since the presumption is that you're innocent, if the defense can poke holes in the prosecution's case, enough that the jury isn't 100% convinced that you absolutely did it, they have to acquit.
But if you walk into a court where everyone already thinks you're guilty, it's going to be a lot harder for the defense to raise reasonable doubt, and the burden of proof is going to essentially be lifted from the prosecution, because they're just proving something that the jury already thinks is true.
So when the police and the Mayor of New York keep going out of their way to present Mangione as guilty in public (the perp walk, having 4 officers behind him at the arraignment, as though he's a danger to society, not saying "alleged"), they are convincing the public that he's guilty before a trial even starts, and it's going to be difficult to find an unbiased jury. If the jury is made up of people who think he's guilty before it starts, he doesn't get a fair trial.
So it's not gaslighting to ask if we actually know it's him... we don't know, and people very much need to keep remembering that.
None of us were eyewitnesses. The CCTV footage doesn't show his face. We didn't see the police find the alleged evidence on him. We haven't seen this evidence in person. We have not heard any sworn testimony. We have not heard a confession.
We very much do not know that he did it. People are literally only assuming he did it because they've been told that he did. They're accepting it without proof, and that's dangerous.