He is very quiet, creepy and manipulative and can easily be compared to the likes of Hannibal Lecter. Early dialog implies that at one point he was hired as a mercenary to burn buildings possibly for insurance schemes. He was also creative in his attacks as he was even know to rig telephones to explode by "taping kitchen matches to the bell strikers, wrapped in gasoline soaked cotton balls". He was once caught in one of his own fires and was saved by Donald "Shadow" RImgale (then a fire fighter) who apparently was unaware of who he was. Rimgale accidentally ran into a barrel of phospherous which exploded, badly scarring them both.
He is imprisoned in the film and his chances of parole are always thwarted by Donald Rimgale, now an arson detective. Rimgale drops a burned doll on the table in front of him at his parole hearings asking "What did do to that little girl?" To which he coldly replies " I burned her...". This comes after Bartel lied to the parole board that he was "ready for society". When asked what he would like to do with the world, he replies "Burn it all!" indicating that he is a true anarchist.
Who doesn't Love Fire?
Later, he is visited by firefighter turned-apprentice arson detective, Brian McCaffery who seeks his knowledge of fire to obtain information on an arsonist he is trying to stop. Bartel shows him an old copy of a Time magazine which has McCaffery's picture, as a child, on the cover. Bartel has already deduced who the arsonist is and begins to taunt McCaffery. Bartel refuses to reveal the information until McCaffery explains who is on the cover of the magazine and if the fire that his father died in "looked at him". McCaffery indicates yes which amazes Bartel, who then begins to explain the clues to the arsonist's identity: The arsonist hates fire but uses it and is around the chemical, Trictachloride for long periods of time. Brian realizes to his horror who the arsonist might be. Bartel leaves off by saying "That wasn't such a long walk after all?"