User blog comment:KuraiJack/Romans plan./@comment-13879303-20130928035908/@comment-10390252-20130928134808

Actually, it might be Velvet or possibly Port. What better way to deliver a crushing blow to the characters' innocence than by introducing a likable new character and then killing them off? It would help establish that this is a pretty dangerous world, kids - people are dying out there! It is also a useful (if rather crude) character development driver.

Team CRDL might be on the quick road to explusion - Jaune beats up Cardin and, in revenge, they decide to work over Velvet. They are a bit too... enthusiastic and have no choice but to flee before Ozpin can hand them over to the authorities. This works because naming Cardin for the man who effectively killed Joan of Arc somehow doesn't work for what is no more than a schoolyard bully right now. However, as Jaune's arch-enemy, the renegade Hunter, the name works a lot better.

The use of the term 'character' suggests that it is someone we've seen on-screen rather than someone whose existence is inferred but has never been seen (such as Ruby and Yang's parents). That said, I haven't seen this tweet either and the OP is vague enough that the term 'character' might be a misunderstanding and all Monty was doing was warning of an on-screen death. We might just see Crimson personally killing someone (for the evilulz) to establish that she's a dyed-in-the-wool baddie.