As Michael Jackson fans continue to flock to Neverland and Staples Center, where a memorial service will be held Tuesday, behind the scenes, investigators are tracking how the pop singer got prescription drugs — and from whom.

No information has been released from two autopsies conducted on the King of Pop, but speculation continues to focus on the possibility of a drug overdose, and specifically on the anesthetic propofol, which investigators reportedly found at the Holmby Hills mansion where Jackson went into full cardiac arrest June 25.

Propofol, marketed under the brand name Diprivan, is a strong anesthetic used in surgical and clinical settings.

Because of its milky-white consistency and powerful effects, the medical
community has nicknamed the drug "milk of anesthesia" or "milk of amnesia," according to the Los Angeles Times.

Last weekend, police detectives questioned Jackson's in-house doctor, Dr. Conrad Murray, who was at the home when Jackson stopped breathing.

Murray's attorney, Ed Chernoff, said the doctor had nothing to do with the pop star's death and will fully cooperate with investigators.

"He is not a suspect but a witness," he said.

LAPD Officer Rosario Herrera confirmed that investigators questioned Murray and said he was cooperating.

However, medical experts pointed out that Murray is an anesthesiologist who could have had access to propofol, which is not meant for home use.

Randy Phillips, chief executive of AEG Live, which was producing Jackson's series of concerts in London, earlier told a Houston television station that Jackson had demanded that Dr. Murray be added to Jackson's payroll.

Demerol and OxyContin, also known "hillbilly heroin," are among the other painkillers that Jackson was allegedly using.

According to CNN, the entertainer owed $100,000 to a drugstore.

As with many celebrities, it is believed Jackson got painkillers through multiple doctors and by using multiple names.

A registered nurse told CNN and other news outlets that while working for the singer in April, he begged her to provide him with propofol to help him
sleep.

The celebrity gossip Web site TMZ.com reported that Jackson "made the
rounds" at Los Angeles doctors' offices, often getting anesthesia for minor
outpatient procedures that do not normally require painkillers.

According to TMZ, Jackson got painkillers under various names, some of
which have turned up in the database.

The Web site cited anonymous sources who said Jackson's body had
multiple injection marks, and that he used a slew of aliases, including Omar
Arnold and Jack London, along with the name of a bodyguard and the office manager of one of his doctors, to obtain prescription medications.

Both the U.S. Drug Enforcement Administration and the state Attorney
General's Office have joined the investigation into Jackson's death.

State investigators are using a computer database to mine for information on prescription drugs to be passed on to investigators with the LAPD's Robbery-Homicide Division.

The database contains the name of doctors who have prescribed controlled
substances, the names on prescriptions, the quantity and date.

If it turns out that Jackson died from a painkiller, and investigators
can track the drug to a specific doctor, it's possible the physician could face
manslaughter charges, TMZ noted.