I think Lizzy know something but she wouldn't have kill Agni Yukitsuke
I think there were two people who attacked Agni and Soma, Lizzy is the gunner but the one she was with who stabbed Agni to death is the killer. I just posted my theory based on chapter 126-128 :)
I'm wonder why he suddenly said to Sebastian "you wouldn't lie to me?"
Like if he have suspicion for something