Genuine question, but supposing we were to consider this theory, why would there also, one, be complaints about the cops parading him around as a victory, and two, people saying Luigi was a hero?
Whether you love or hate cops, they are not stupid. I'm sure if there was even an ounce of suggestion that they got the wrong guy, the cops would quietly decide not to be so smug about it.
And to those who side with him, he's either a hero/idol or he didn't do anything. Pick one. I myself pick the third choice.
Also, of note, it's quite a coincidence they found the guy, then found out his name, and then found out his wealthy upbringing, evidenced by the fact he was trying to be as low profile as possible at the time, which would've curbed the ability to do all of that in reverse order. If he wasn't the killer, that's like firing a bullseye in the dark.