Advice on Coterie committing diablerie? [V5]

Edit: Thank you all for the invaluable information and perspectives. I'm gonna work with the table to see what options we have going forwards

Hey all. I'm very new to this Vampire thing so I don't know the lore or how people should react to this stuff but a member of my Coterie committed diablerie on a kindred that was staked (but otherwise was no threat) simply because he was mad (he's a Tremere)

We're in Anarch territory but I don't know how I should react to this in-character, like is it a case by case basis or just universally bad? As far as I know the diablerist didn't take a stain and instead just got some new powers, no consequences that the group knows.

Another player told the Baron's secretary about it and no longer trusts the character. What would be the in-universe response? My initial thought was to wait for the Baron's response and if he wants us to, bag the diablerist and deliver him to the Baron but like that feels like a PvP mentality no?