Michael Jackson's personal doctor gave him a powerful anesthetic through an intravenous drip to help him sleep, and authorities believe the drug caused the pop singer's death, a law enforcement official told The Associated Press. The official said Jackson regularly received the anesthetic propofol and relied on it like an alarm clock. A doctor would administer it when Jackson went to sleep, then stop the IV drip when the singer wanted to wake up. On June 25, the day Jackson died, Dr. Conrad Murray gave him the drug through an IV sometime after midnight, the official said. Murray's lawyer, Edward Chernoff, has said the doctor "didn't prescribe or administer anything that should have killed Michael Jackson." When asked Monday about the law enforcement official's statements he said: "We will not be commenting on rumors, innuendo or unnamed sources." In a more detailed statement posted online late Monday, Chernoff added that "things tend to shake out when all the facts are made known, and I'm sure that will happen here as well." Toxicology reports are still pending, but investigators are working under the theory that propofol caused Jackson's heart to stop, the official said. Jackson is believed to have been using the drug for about two years, and investigators are trying to figure out how many other doctors administered it, the official said.