In the early 1800s, Inquisitor Dearborn brutally interrogated Annabel Blackthorn in order to obtain Malcolm Fade's location, as he had stolen the Black Volume of the Dead. When it became clear she didn't know anything, Dearborn had her sent back to her family—tortured and half-mad—to say goodbye before being sent to the Adamant Citadel. When the Iron Sisters sent word that she never arrived, Inquisitor Dearborn visited Annabel's family to query her whereabouts.
After speaking with Felix Blackthorn Dearborn suspected that Annabel was dead and proposed a trial by the Mortal Sword for her father. When one of the Blackthorns questioned why Dearborn cared so much, considering the condition Annabel was returned in, he brushed it off, saying she was no more hurt than any Shadowhunter may be in battle. Dearborn ultimately ended the search for Annabel after one of Felix's Herondale friends pointed out how well the illusion of her being an Iron Sister benefited the Shadowhunters.
Dearborn was a corrupt Inquisitor. He showed no regard for justice as he was willing to ignore Annabel's murder by her family, despite it being a major crime, if it benefited him and Shadowhunters as a whole. He also showed the typical disgust towards Downworlders as other Shadowhunters of that time and was quite cruel, as he tortured Annabel and showed no remorse for it.
Inquisitor Dearborn was a youngish man with dark hair.
- Lord of Shadows (flashback)