Drugs (pigment), duty work
Craig was an undercover FBI agent sent by his superiors to infiltrate the Orpheus Group in an attempt to prove the whole thing was an elaborate scam. Getting a position as a trainer put Craig face to face with the truth: there were ghosts out there. He enjoyed his second job so much he decided to take the pigment offered by a co-worker. He ended up hooked, and decided to reveal who he really was in hopes they might have a treatment for him. Impressed with his field record, Orpheus hired him on as an agent of their own, but never offered him the solution he hoped for.
When his superiors found out, they were furious. They sent a team in to retrieve Craig, believing him brainwashed by the drugs. When he resisted, the team used more force. It turned out to be too much force; Craig, high on pigment, couldn't take the strain and died because of his former friends and allies. He became a hue, and continued to work for Orpheus.
When Orpheus was destroyed by NextWorld, he and fellow ghost Annie Harper followed their living counterparts into fugitive hood, though as spirits they had more of a range of movement. They continued working with them when Lazarus Redux was founded.
While out on a training mission with Chet Mason and Ben Cotton, a huge piece of a watchtower pierced the Stormwall, causing an enormous quake in the worlds of the living and the dead. When attempting to rescue other ghosts from the tower and the area around it, Spectres poured forth from the structure. Craig, trying to rescue a victim, ended up swarmed by them, and sent his last bit of Vitality to Chet and Ben before being shredded by Spectres. He sacrificed himself to save them, a scene that haunted Mason for weeks after the incident.