[ TBH YOU RIGHT... things I should have thought about weeks ago but didn't because I DIDN'T EVEN KNOW A REVOLVER ISN'T A PISTOL. ]

There's an annoying amount of options here.

G'raha and Sariel were also both in the tea room and have to have left at some point. The killer could either have been in the room with us, or they could have entered after they left.