Dease's backstory itself is shrouded in both mystery and violence, with the information that can be uncovered on him proving to be the stuff of horror films - which is fortunate, since that's exactly where we're at. Vetril Dease is revealed to have had a hell of a life, both suffering and causing his own tragedies along the way.
In a debriefing with the private investigator, Tom learns that Dease was put into an orphanage when he was a child due to his father enacting 'cruelty beyond the bounds of humanity', with Dease and his dad being the only survivors of a suspicious house fire that killed his mother and sister.
Once he turned 18, he was allowed to leave but suffered an intense breakdown - causing him to track down his father and murder him as an act of revenge for the abuse he suffered. That wasn't before he tortured him for days, however, finally burning him alive and spending 20 years locked away in a psychiatric hospital for the criminally insane as a result.
No normal hospital, this one rendered its patients 'human guinea pigs', using them for medical experiments involving injections, shock therapy, and other unthinkable traumas. A court case managed to release those incarcerated there - at which point Dease left for LA, got a job at a veterans home, and disappeared from public records, aside from one co-worker who knows his temper is murderous from a mysterious death linked to a man that treated Dease disrespectfully at the home.
Living in his apartment block above Josephina, Dease poured his trauma into his paintings, using his own 'tissues', aka blood, to form pieces that have a supernatural effect on the viewer and their subsequent interactions with other pieces.