L.A. County Sheriff Lee Baca claims there was simply no room at his jail for a "low-level offender" like Paris Hilton -- and her "severe" medical problems were only getting worse.
In a statement to the press, Baca said, "There's 20,000 inmates -- the largest jail system in the United States ... It's very overcrowded."
According to Baca, 90% of the inmates in L.A. County jail are serious felons -- many held on murder charges or attempted murder charges. Paris was one of the "low level" offenders -- who usually serve 10% of their sentences.
Baca also said that he reassigned Hilton based on "her severe medical problems," and confirmed TMZ's original story that her condition was mental. Baca said that her "increasingly deteriorating problems" were evaluated and added, "This lady has some severe problems."
Baca added that she was medicated when she originally entered the jail system ... and "I can't trust her tenuous status," referring to her mental state. "She had a severe problem," said Baca, "I need more cooperation from the courts and from the city attorney's office."
For now, Baca says he will comply with the court order and keep her behind bars -- "If there's any further deterioration, hopefully we'll be able to address it."