Board Thread:Questions and Answers/@comment-25086462-20180731225644/@comment-36460284-20180804091314

Armin's parents were killed by Djel Sannes (the same man who killed Pastor Nick and Erwin's father and was tortured by Hanji and Levi) when they tried to escape the walls and discover the world beyond Wall Maria using a hot balloon. Armin was either lied to when they informed him of his parents' death or he deduced the reason behind their killing but was afraid to speak.