Minstrum Yerin: We don't know. but we suspect Vanguard agents, of course. In the chaos of the evacuation, the soldiers had their hands full making sure no one was trampled, and that looters were promptly apprehended. When we visited the temple after everyone had left -- there were so many books and valuable artifacts we wanted to bring here, for safe keeping -- we found Tobias by the murals he loved so dearly. He's been stabbed in the heart, and from the looks of it, he didn't resist much at all. He probably even knew his assailant.
April: Why Tobias? He was the kindest, gentlest man I've ever known. Always helpful, always ready to listen. I'll really miss him.
I had forgotten this part. Someone Vestrum Tobias knew? My best guess is that it was Brian Westhouse. There is something shady about him, specially considering the events on Dreamfall.