Janet Jackson arrives for a manslaughter hearing against the doctor who treated her brother Michael before his sudden death (PHOTO).

Janet Jackson arrives for a manslaughter hearing against the doctor who treated her brother Michael before his sudden death (PHOTO). (KTLA-TV / January 10, 2011)

Prosecutors testified during opening arguments that Jackson was already dead when Murray called for help.

They say Murray waited at least 9 minutes to call 911, possibly longer, and failed to mention the propofol to paramedics and doctors at UCLA Medical Center.

The defense was expected to argue that Jackson killed himself by injecting more of the sedative.

The hearing, which is expected to last 7 or 8 days, will determine whether Murray will stand trial in the pop star's death.

Both sides have clashed over who should test residue from two syringes found in Jackson's bedroom. Liquid in one of the syringes has already dried up and was now "salt," according to attorneys.

Defense attorney J. Michael Flanagan said he would not comment on any defense strategy and said lawyers were still in investigating the case.

Flanagan, however, did tell the judge the syringe may have been used by someone other than the doctor to administer the powerful anesthetic that caused Jackson's death June 25, 2009.

Defense attorneys want tests to be performed on the syringes and an IV bag found in the singer's mansion after his death, saying they are rapidly deteriorating and could provide vital information in the case.

A judge has approved a plan to allow defense lawyers to test the syringes and the IV bag.

Flanagan has alleged that coroner's officials should have done "quantitative" analysis of the items to help determine "the means of who injected Jackson" with the powerful drugs that killed him.

Flanagan said a huge amount of the anesthetic propofol was found in Jackson's body but his client has said he gave him only 25 milligrams on the drug.

Deputy District Attorney David Walgren suggested that the defense will claim Jackson killed himself by injecting more of the drug into himself.

Quantities of substances in the syringes and IV bag could be crucial to explaining how the singer died, according to lawyers. The testing could determine the quantities of drugs in the items, which the cardiologist's lawyers say is crucial information for trial.

Defense attorney Ed Chernoff says substances in one broken syringe found at the mansion had dried up since June 2009, when the judge ordered the evidence preserved. The tests sought by Murray's attorneys will destroy the samples and can only be performed once.

Tissue samples in Jackson's body were tested for levels of various substances and led to the coroner's determination that the pop singer died in part from acute propofol intoxication.

The anesthetic is supposed to be administered in hospital settings, but Murray told investigators he had been providing it to Jackson as a sleep aide and had been trying to wean him off the drug.

Chernoff has said the doctor did not give Jackson anything that should have killed him.

The tests are likely to be conducted by the Los Angeles County coroner's office.