The world is not reducible to "So what? Democrats are worse." If it were drugs, or shoplifting, or even an outburst of violence that remotely resembled "fighting," I got no problem. If it had been this, and he had said the incident had haunted him and he regretted it deeply, fine.
He claims to be the only person involved who has not struggled with that incident ever since. He is not only untroubled, he claims not to even remember. And he was the *instigator*.
If he's lying, well then he's a liar and a coward. If he's telling the truth, he's a sociopath.