"It becomes nothing more than manslaughter or something worse than that," he said.
Propofol, known by the trade name Diprivan, was among the drugs removed from Jackson's rented mansion, according to ABC News sources.
Meanwhile, federal drug-enforcement authorities contacted the makers of Diprivan as part of their investigation into Jackson's death, according to the Associated Press.
"He was not in terrible pain when I saw him. He danced in the office, and he danced for my patients," Klein said. "He was very muscular, and he was very, very happy and dancing." "I saw nothing at that point that would make me worry whatsoever," he continued. "But I was always concerned about him because I was always worried about other doctors."
Klein was not the doctor in Jackson's Los Angeles rental home, when he died on June 25. That physician, Dr. Conrad Murray, is also being questioned by the authorities.
The coroner has yet to supply an official cause of death for Jackson, pending the results of a toxicology screening.