Vincent just… stares for a moment, processing what Robert was saying slowly. What was he trying to say, with that…? Why bother to regret it…? He was damned no matter what…? Was he seriously suggesting Vincent shouldn’t even-
I’d do it all again.
Vincent looks dizzy at that, head reeling and stomach twisting in a way that makes him have to actively resist dry-heaving. He raises an arm (with some difficult) to the cell doorway to steady himself, though that only makes it feel more claustrophobic in here, more… ugh.
CW for vague suicidal implications (just in case)

“Of course it wasn’t worth it for me. Why would it- I… I’d rather have died than ever kill her, I don’t know why I did it.”
He’s said that already, he’s repeating himself now, not even looking at Robert but rather some point in the distance vaguely near him.
This wasn’t an interrogation. Not in the legal sense, unless Robert was somehow a very skilled undercover cop, and not even in the conversation sense either. Robert was just… asking. It was reasonable to want to know how much of a threat he was.
The voices in his head, on the other hand, were certainly having a field day, repeating and even going beyond his own thoughts again and again in a chorus. Even Suzune realized it before, after she saw what you did. You’re DANGEROUS when you’re upset.
Vincent closes his eyes tightly and grimaces, trying and failing to ignore the whispers. There were some voices that he could recognize were wrong, that seemed to try to twist things into something it wasn’t, but- So many of them felt like they were right, too.
“…I lost control. We were just… talking, in the kitchen. Arguing. It wasn’t even- It shouldn’t have led to that, but I grabbed a knife, and escalated things. I killed the person I was meant to cherish most.”
Vincent’s voice sounds a little dead, admitting that, but at least he didn’t sound frantic anymore. He takes a slow breath, and opens his eyes, looking down.

“It’s not only God that shouldn’t forgive me, I’m not worried about going to Hell, even if I’m sure I will, personally. I don’t think I can forgive myself, either. But I know that if I tried to get away with it, if I hid what I did and just carried on with my life, I really wouldn’t be able to live with myself.”
He can’t bring himself to judge Robert for clearly trying to do that himself, of course, not with the sheer guilt he’s still working through himself and the knowledge that their cases were… very, very different despite some things seeming similar on the surface. This was purely about himself.