(FOX News) -- What drove Las Vegas gunman Stephen Paddock to shoot up a country music concert remained a mystery Tuesday, as a vexing array of possible clues did little to bring into focus a motive for the biggest mass shooting in modern American history.
Mounting gambling debts, a family history of mental illness, partisan political rage and a claim of responsibility by ISIS have all emerged as possible motives for Paddock's Sunday night shooting spree on Sin City's fabled Strip, which left 59 dead and more than 500 injured. But police - as well as the few who knew Paddock - remain stymied as to what caused the 64-year-old former accountant to snap.
"I can't get into the mind of a psychopath," said Sheriff Joseph Lombardo, head of the Las Vegas Metropolitan Police Department.
Paddock had 23 guns in his hotel room, including rifles with scopes and two modified to make them fully automatic, along with 19 firearms at his home in Mesquite, Nevada. Police are searching another property Paddock owned in northern Nevada.
While each theory appears to have at least some basis in fact, they also have factors that would seem to cast doubt and have left investigators with more questions than answers.
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