Under heightened security, Murray was driven into a secure garage - insulated from Jackson fans who have in the past hurled insults and blame.
Willie L. Hampton, one of Murray's patients, said he came to court in support of his friend.
"He is upset about Michael, he's upset about the media and what some people are saying," Hampton said.
To gather an impartial jury, the court summoned 450 people. The first 185 were introduced to the defendant and the attorneys in an assembly hall turned into a courtroom. When asked if there was anyone who had not heard of the trial, not one person raised a hand.
"Those jurors should never sit on a case like this," said legal consultant George Bird. "Those jurors are not going to be listening to the facts and making decisions from the facts. They have preconceived notions that they are not going to set aside."
The court dismissed 113 prospective jurors who would face hardships serving on the 25-day trial. That left 72, who filled out a 30-page questionnaire that included questions like whether they had bought Jackson CDs.
"Jurors experience with drugs, or people that have been disciplined, or people that have professional licenses that have been disciplined," said Bird.
A single reporter was allowed inside the proceeding.
"He sat there looking very somber, looking straight ahead, showing no reactions," said Linda Deutsch of the Associated Press.
Superior Court Judge Michael Pastor delivered several admonitions about reading any coverage of the case, and also told jurors they were not to Tweet about the trial or read Tweets about the trial.
Potential jurors will be narrowed down to 100 who will eventually be questioned by attorneys on Sept. 23.
It will be the second time this year that a judge, prosecutors and attorneys try to pick a panel to hear the case, which will put the spotlight on the King of Pop's final moments once again.
Murray's attorneys had asked for the jury to be sequestered, but the motion was denied by the judge on Wednesday.
The final jury will decide Murray's fate, charged with involuntary manslaughter in Jackson's 2009 death. Murray, who was Jackson's personal physician, is accused of injecting deadly amounts of the sedative propofol into the singer.
Defense attorneys say Jackson took the drug on his own orally. The judge has allowed prosecutors to introduce a study showing whether propofol has any effect if ingested orally as the defense claims.
Opening arguments in the trial begin on Sept. 27.
Jackson death stunned the world, as the singer had been getting ready for a series of comeback concerts in London.
The Associated Press contributed to this report.