LOS ANGELES (KTLA) -- Round two of the battle of the propofol experts started Thursday afternoon in the trial of Michael Jackson's doctor as the defense anesthesiology expert began his testimony.

When Dr. Paul White continues his testimony Friday, and he is expected to counter the conclusions of prosecution anesthesiologist Dr. Steven Shafer, whose earlier testimony spanned more than a week of Dr. Conrad Murray's involuntary manslaughter trial.

Dr. White said that after reviewing the reports, evidence and analysis from investigators in Jackson's death he was not convinced Dr. Murray was responsible.

"I was somewhat perplexed at how a determination has been made that Dr. Murray was infusing propofol," White said. "It wasn't obvious to me, I thought there were questions."

A drug-addiction specialist testified earlier Thursday that Jackson was "probably addicted" to a powerful painkiller given him during frequent visits to a Beverly Hills dermatologist in the three months before his death.

Dr. Robert Waldmon was called by the defense in an effort to show Jackson's insomnia the day he died could have been caused by withdrawal from Demerol shots he was given along with botox injections, treatments that Dr. Murray didn't know about.

White, who is the last witness before the defense rests, spent most of the first two hours establishing his credentials as one of the world's foremost experts on the surgical anesthetic propofol, which the coroner ruled was the chief drug that killed Jackson.

The personal and professional rivalry between Dr. White and Dr. Shafer played an odd role in Thursday's testimony.

White's longtime friendship with Shafer has been tested during the Murray trial, including an incident last week that resulted in the judge scheduling a contempt-of-court hearing against White for next month.

At one point Thursday, White suggested someone "tell Dr. Shafer he needs to learn how to spell plasma," because it was misspelled on a graph he created.

White, however, attempted to downplay rivalry with Shafer when the judge mistakenly called White "Dr. Shafer" for a second time. "I take it as a compliment, actually," White said.

White and Shafer, who are on opposite sides in this trial, may have a new anesthesia product to develop as a result of their preparations to testify, White said.

Both experts commissioned studies on the possibility that Jackson might have orally ingested the fatal dose of propofol, something they both have now ruled out. But they learned that propofol could be absorbed through the tissues of the mouth, White said.

He and Shafer agreed during courthouse chats while waiting to testify that they might be able to develop a propofol lollipop as a "non-invasive sedation device."

Shafer testified last week that he concluded the "only scenario" that fits the scientific evidence is that Jackson was on an IV drip of propofol for three hours before his death and that Murray failed to notice when he stopped breathing.

Shafer conceded that it was possible that Jackson, not Murray, could have been the one to open the drip to a fatal pace, but prosecutors contend it would make no difference in Murray's guilt.

The defense hopes the testimony from White and Waldmon, their last two witnesses, will convince jurors that Jackson gave himself the overdose of drugs that killed him while Murray was not watching.

The Los Angeles County coroner ruled Jackson's June 25, 2009, death was the result of "acute propofol intoxication" in combination with several sedatives.

The defense theory is that a desperate Jackson, fearing his comeback concerts could be canceled unless he found elusive sleep, self-administered propofol that Murray was trying to wean him off of.