Michael Jackson likely injected himself with a fatal dose of the anesthetic propofol after popping an extra eight sedatives without his doctor's knowledge, a Los Angeles court heard on Friday.

Dr. Paul White, the last defense witness in the involuntary manslaughter trial of the singer's physician, Dr. Conrad Murray, said that self-administration was the most likely scenario to explain levels of propofol and lorazepam found in Jackson's system after his death on June 25, 2009.

White said that based on the amount of propofol found in Jackson's urine, he believed the pop star gave himself a further injection of propofol about one hour after Murray has admitted injecting the 50 year-old singer with a relatively small 25 milligram dose of the drug as a sleep aid.

With the administration of the additional 25 milligrams that we're speculating was self-injected by Mr. Jackson, the level increases rapidly and at the time of death would be almost identical to the level found in the urine at autopsy, White told jurors.

Using a mathematical model, White also said Jackson could have swallowed eight lorazepam tablets earlier in the night as he struggled with sleeplessness, bringing the amount of the sedative found in his blood to that seen at autopsy.

The combination effect is potentially profound, White said of the two drugs.

Authorities have ruled Jackson died of an overdose of propofol, with lorazepam playing a contributing role.

A rival expert testified for the prosecution last week that he believed Jackson died after Murray left him on an intravenous drip of propofol for a number of hours.

But White said there was no physical evidence at the scene to support the prosecution scenario. It also did not reconcile with Murray's statements about the amount of drugs he gave Jackson that night, White said.

Prosecution experts will cross examine White on Monday as the five-week trial enters its closing stages.

White on Friday questioned the mathematical modeling prepared by prosecution expert Dr. Steven Shafer to support the intravenous propofol drip theory.

In order to reach the blood level of propofol found at autopsy, Jackson would have had to stop breathing right as the last drops fell from a 1,000 milligram bottle of propofol given with an IV drip, White said.

White called Shafer's hypothesis an incredible coincidence of circumstances.

Murray denies involuntary manslaughter but could face up to four years prison if convicted. His attorneys said earlier this week he will not testify in his own defense.

Murray told police he had been trying to wean Jackson off his dependence on propofol. But he claimed the singer begged him for the drug the day he died.

Prosecution witnesses have also testified that Murray delayed calling emergency services, failed to tell ambulance and hospital staff about the propofol, and say he should never have been giving Jackson the drug for insomnia at all.