Jason told Rene about his death and how it still affects him.
After Joker escaped from Arkham again Bruce expected to be confronted with the clown soon enough especially with how hidden he's been. Fast-forward investigation Bruce (or anyone in the batfam / the GCPD) finds a body in a wearhouse, tied with cuffs to a support beam, burned to a crisp, with Joker colored clothes (or what remained of them).
A DNA test shows that this is in fact Joker's corpse and now an investigation about who could have done it is in working, mostly because whoever did it didn't leave any traces behind.
Gothamites are celebrating and Jason is right there with them. The only reason he would want the culprit to be found is to meet his new favorite person.
Jason: "I don't think I've been this happy since I was revived!"
Rene: "Really? That's kinda depressing but glad to hear it I guess."
Jason: *jabs them* "Shut up."
Rene: "Hehehe, you saw the body right?"
Jason: "Yeah, burnt to the bone in some places. With gasoline, I think Bat said."
Jason: "Yeah you do not wanna see that. Glad his last moments were painful."
Jason: *nods* "I wander what the reason was. With his record it can be anything really."
Rene, who remembers how Jason almost had a breakdown talking about him and how sometimes he can only hear manic laughter and can't sleep without waking up in cold sweat.
Rene, who took one of Jason's gas canisters and he didn't even notice, and when he did he figured he forgot to refill it.
Rene, who kept a close eye on the joker ever since he escaped Arkham to catch him alone and by surprise.
Rene, who's disguise was a black curtain they found and wrapped over themself paired with cheap blue hair extensions to be seen coming out from under the hood in case of any cameras.
Rene, who still feels sick from hearing someone scream in agony and burn alive, even if he deserved it.
Rene, who will still feel sick from smelling anything burning, especially meat, for quite a while from now on.
Rene: "Too many bad jokes?"
Jason: "Pfff– yeah right."
Rene: "I can see it. Dude was never even funny even though he chose to be a clown!"