So going off FF logic this is what I am taking off of the events of the night.

A girl was the killer.

The old man may have been Cid, Seifer knew him and Cid was the SeeD head master.

The man in the White Armor could be be Cecil, Firion.

There is a few more things I am wondering about as either Fynn wasn't alone, or the person watching him was with someone else.