In a report filed by the GCPD, there were three theories that were presented for the Joker’s origin and identity. The first was that the Joker was institutionalized as a patient at Arkham Asylum who got released when his scars were almost healed or escaped during Ra’s Al Ghul’s and Scarecrow’s reign of fear with all the other patients at the time in an even worse condition (perhaps due to Scarecrow’s terrible methods), which explained why most of Joker’s Henchmen were identified as some of the Arkham escapees. However, that theory was debunked on the basis that Joker’s identity had no basis within any records.
The second theory was that the Joker worked as a disgruntled employee or attraction for the Haley Brothers Circus, which was documented to have connections with the mob and explained the clown makeup that Joker always wore for his persona. The third theory that was presented was that the Joker served as a soldier or Army Private until he was sent home because he suffered from acute PTSD, which explained his cool demeanor and familiarity with weapons, as well as his devastating effectiveness in various forms of combat . The third theory is further supported by his anecdote to Harvey Dent about how if a mayor is killed by him it causes an uproar yet barely anyone cares should he arrange for a truck containing soldiers to be blown up.
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