Prosecutors this week begin offering evidence that Michael Jackson's doctor is responsible for the pop star's death in a case that could hinge on who gave the singer a fatal dose of a powerful drug he used for sleep.

Dr. Conrad Murray, Jackson's physician in 2009, has been charged with involuntary manslaughter in the death, and a Los Angeles judge on Tuesday starts the preliminary hearing -- largely seen by legal experts as a formality -- to determine if enough evidence exists to bring the physician to a full trial.

Jackson, one of the best-selling recording artists of all time who generated hits like "Thriller" and "Billie Jean," died of a prescription drug overdose on June 25, 2009, at age 50, after suffering cardiac arrest while in bed at his rented mansion.

Murray has admitted injecting Jackson with the powerful anesthetic propofol, which has been determined to be a key factor in his death. The drug is used mostly in hospital settings, but it was given to Jackson at home as a sleep aid.

Prosecutors hope to paint the doctor, who was hired by a concert promoter to care for Jackson before a series of performances, as a man who was in financial trouble and would irresponsibly give the singer drugs to keep his paycheck.

Murray has pleaded not guilty, and last week defense attorneys indicated they may focus on a mysterious syringe found near Jackson to explore whether someone other than Murray injected the singer with the fatal dose of propofol.

Some experts are skeptical about that possible defense, which is based on the assumption that Jackson, an admitted drug abuser, could have administered the propofol to himself.

"It plays to what people perceive Jackson was about and that he might have done it, but it's hard to see how it occurs without Murray having some role in it," said Laurie Levenson, a professor at Loyola Law School.

PRELUDE TO A TRIAL?

Last week, Los Angeles Superior Court Judge Michael Pastor cleared the way for the defense to test residue from syringes and an intravenous tube used to administer drugs to Jackson.

Following Jackson's death, the Los Angeles County coroner determined that propofol and the sedative lorazepam were the main drugs that caused Jackson's death.

In their investigation, police and prosecutors focused on Murray and whether he had given Jackson too many drugs when the doctor should have known better.

Evidence in Jackson's death has been outlined in search warrant affidavits, but prosecutors will present more of their case against Murray in the preliminary hearing, which the doctor's attorneys say could last two weeks.

That would be even longer than the one-week preliminary hearing for football great O.J. Simpson's notorious 1995 trial on a charge he murdered his ex-wife, Levenson said. Most preliminary hearings in Los Angeles last a few hours at most.

In the end, the judge in the Murray case is largely expected to order a full trial because the burden of proof on prosecutors is low at a preliminary hearing.

Legal experts also see obstacles to any last-minute plea deal between prosecutors and defense attorneys.

"It sounds to me that this is going to be a trial," said Bennett Gershman, a former New York prosecutor. "There's just too many close factual questions that don't seem like they're going to be resolved by some kind of plea."

Steven Cron, an attorney who teaches at Pepperdine Law School, said Murray's lawyers may pursue a different defense if the case does go beyond the preliminary phase. If that occurs, Cron said testimony of medical experts will be key given that Murray was alone with Jackson in his last waking hours.

"It's going to be a case of dueling experts. Whose expert is more credible and why," he said.