Lawyers for Michael Jackson's doctor dropped the bombshell they had been hinting at for months - an expert opinion accusing the legendary singer of causing his own death.

Dr Paul White, the defence team's star scientific witness, said Jackson injected himself with a dose of propofol after an initial dose by Dr Conrad Murray wore off.

He also calculated that Jackson, 50, gave himself another sedative, lorazepam, by taking pills after an infusion of that drug and others by Murray failed to put him to sleep.

That combination of drugs could have had "lethal consequences", the researcher said.

Murray, who had been hired as the singer's personal physician for his This Is It tour, has pleaded not guilty to involuntary manslaughter over Jackson's death in June 2009.

Dr White showed jurors at Los Angeles Superior Court a series of charts and simulations he created in the past two days to support the defence theory. He also did a courtroom demonstration of how the milky white anaesthetic propofol could have entered Jackson's veins in the small dose that Murray claimed he gave the insomniac star.

Dr White said he accepted Murray's statement to police that he administered only 25 milligrams of propofol after a night-long struggle to get Jackson to sleep with infusions of other sedatives.

"How long would that (propofol) have had an effect on Mr Jackson?" asked defence lawyer Michael Flanagan.

"If you're talking effect on the central nervous system, 10 to 15 minutes max," Dr White said.

He then said Jackson could have injected himself with another 25 milligrams during the time Murray has said he left the singer's room.

"So you think it was self-injected propofol between 11:30 and 12?" asked Mr Flanagan.

"In my opinion, yes," Dr White said.

The witness, one of the early researchers of the anaesthetic, contradicted evidence by Dr Steven Shafer, his long-time colleague and collaborator. Dr Shafer earlier said Jackson would have been groggy from all the medications he was administered during the night and could not have given himself the drug in the two minutes Murray said he was gone.

"He can't give himself an injection if he's asleep," Dr Shafer told jurors last week. He called the defence theory of self-administration "crazy".

The prosecution asked for more time to study the computer programme Dr White used before cross-examining him.

Judge Michael Pastor granted the request, saying he too was baffled by the complicated simulations of Jackson's fatal dose. He recessed court early and gave prosecutors the weekend to catch up before questioning Dr White on Monday.

The surprise disclosure of White's new theory caused a disruption of the court schedule and the judge had worried aloud that jurors, who expected the trial to be over this week, were being inconvenienced. But the seven men and five women appeared engaged in the evidence and offered no complaints when the judge apologised for the delay.

Prosecutors could call Dr Shafer back during their rebuttal case to answer Dr White's assertions.

Among the key issues is how Dr White calculated that a large residue of propofol in Jackson's body could have come from the small dose that Murray says he administered.

Dr Shafer assumed Murray had lied and he estimated Jackson was actually given 1,000 milligrams of the drug by Murray, who he said left the bottle running into an IV tube under the pull of gravity.

Dr White disputed that, saying an extra 25 milligrams self-administered by Jackson would be enough to reach the levels found in his blood and urine.

Dr White also said a minuscule residue of the sedative lorazepam in Jackson's stomach convinced him the singer took some pills from a prescription bottle found in his room. He suggested the combination of lorazepam, another sedative, midazolam, plus the propofol could have killed Jackson.

"It potentially could have lethal consequences," said Dr White. "... I think the combination effect would be very, very profound."

Dr White's testimony, expected to end Murray's defence case after 16 witnesses, is likely to be challenged vigorously by prosecutors, who spent four weeks laying out their case that Murray was a greedy, inept and reckless doctor who was giving Jackson propofol as a sleep aid in the singer's bedroom.

Experts including Dr Shafer have said propofol is not intended to treat insomnia and should not be given in a home.