Several Drug Enforcement Administration agents entered Dr. Conrad Murray's sprawling home in a gated community while others searched Murray's medical offices in Las Vegas, Global Cardiovascular Associates.
"We are looking for documents" related to the death of Michael Jackson, said Michael Flanagan, assistant special agent in charge of the Drug Enforcement Administration office in Las Vegas. He said federal agents and Los Angles police served search warrants at Murray's house and office.
Flanagan said the warrants were sealed and he was unable to say what documents the agents were seeking.
Authorities had no arrest warrant for Murray, who was at home when the investigators arrived, they said.
A lawyer who has represented Murray in financial cases in Las Vegas, Puoy Premsrirut, did not immediately respond to a message left at her office seeking comment.
Flanagan said staff members at Murray's medical office cooperated with investigators.
Las Vegas police were assisting in the search, said Capt. Brett Zimmerman of the department's vice and narcotics bureau.
Murray was Michael Jackson's personal physician and was with Jackson when he died. Murray, who is based in Las Vegas and is licensed in California, Nevada and Texas, had his Houston office and a storage unit searched last week by DEA agents. Court records show the agents were seeking evidence of whether the doctor committed manslaughter.
Police say Murray is cooperating and have not labeled him a suspect.
Toxicology reports are still pending, but investigators are working under the theory that the anesthetic propofol caused Jackson's heart to stop, a law enforcement official told The Associated Press on Monday. Jackson is believed to have been using the powerful drug for about two years and investigators are trying to determine how many other doctors administered it, according to the official who spoke on condition of anonymity because the investigation is ongoing.
The official said Jackson regularly received 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.
The day Jackson died, 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 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, 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."
Murray, 51, became Jackson's personal physician in May and was to accompany him to London for a series of concerts starting in July.
He was staying with Jackson in the Los Angeles mansion and, according to Chernoff, "happened to find" an unconscious Jackson in the pop star's bedroom the morning of June 25. Murray tried to revive him by compressing his chest with one hand while supporting Jackson's back with the other.
The law enforcement official also provided a glimpse into how the pop star was living in the weeks before he died, describing the room in which Jackson slept in his rented Beverly Hills mansion as outfitted with oxygen tanks and an IV drip.
Police found propofol and other drugs in the home. An IV line and three tanks of oxygen were in the room where Jackson slept and 15 more oxygen tanks were in a security guard's shack, the official said.
Using propofol to sleep exceeds the drug's intended purpose. The drug can depress breathing and lower heart rates and blood pressure. Because of the risks, propofol is supposed to be administered only in medical settings by trained personnel.
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