Mr. Hartmann worked in Kinderheim 511, due to his high-level position in the East German Ministry of Health. Tenma contacted him in order to gain more information about the orphanage and the origin of Johan Liebert. Hartmann was intrigued by Johan's intelligence and his way of manipulating, this led him to make a "monster" of Dieter, a child he was taking care of. In hope to make Dieter more resembling to Johan, Hartmann physically abused Dieter. Tenma discovered the bruises all over Dieter's body and took him to the hospital. Tenma was able to convince Dieter to leave Hartmann for his good. (Source: Monster Wikia)