I dunno if I've ever posted my Mikoto theory here so here goes:
I think Mikoto had the intent, but John did the murder.
We know Milgram doesn't need you to have actually been the direct cause of someone's death; being the inciter is enough (Fuuta, Mahiru, Kazui). So if Mikoto went out with a baseball bat with intent to kill someone, even if John was the one who actually ended up killing innocent bystanders, according to Milgram's rules that never would've happened without Mikoto's intent.
Which explains the apparent contradiction in the way Mikoto is the one who's affected by the restraints but John isn't, despite everything else pointing to John being the one who did it (yes, I believe what he said in Neoplasm). Because the facts of the case don't line up; people (unclear how many) were killed, at night, by a baseball bat. This is information seen in both MeMe and Double, but there are also multiple discrepancies between them: the biggest one being where the murder happened - on the train (Double) vs next to it (MeMe). I think MeMe shows the murder Mikoto intended, after he got off the train, but Double shows the murder John committed, on the train on the way there after Mikoto was overwhelmed at the stress of what he was planning.
Throughout Double, Mikoto is shown with his eye-lights at the top of his eye, and John with them at the bottom. In addition, Mikoto is associated with white windows, and John with dark ones.
And at the end of the song, someone says sorry and it's easy to assume it's John based on the rest of the lyrics, but based on the image...
