He killed you in the very dark and small room beacuse he really thought that you Betrayed Decay of Angels but no, when someone told to him on the phone call that you didn't Betrayed the Decay of Angels, his smile fades away, people think blaming that you're a betrayal is a joke... But no Fyodor killed you, a prank went too far

Fyodor: He looks at you slowly with shocked hoping that you still alive with regret

FYODOR FROM BSD ANIME