LOS ANGELES (AP) -- The differing opinions of two professors on how a powerful anesthetic killed Michael Jackson has left jurors with two scenarios to consider about how the King of Pop died, and in the process has also strained the relationship of the two longtime collaborators and friends.
Armed with decades of experience, IV bags and syringes, the men showed jurors how a powerful, milky-white anesthetic may have flowed from a bottle into Jackson's body on the morning of June 25, 2009.
Doctors Paul White and Steven Shafer worked alongside each other for years and are credited with helping bring propofol to operating rooms and making its usage safe.
But their different theories on how Jackson died from the drug -- whether his personal physician Conrad Murray administered it or the singer injected it himself -- have sparked a clash of harsh rhetoric between the two men more familiar with operating rooms and classrooms than the high stakes of a celebrity trial.
White and Shafer were colleagues at Stanford University and conducted research on propofol before it was approved for use in U.S. operating rooms in 1989. Both help edit a leading anesthesia journal. Until White's retirement last year, both were practicing anesthesiologists.
Each man's search to explain how Jackson died led them to conduct their own research and computer modeling.
The tension between them began after Shafer, an affable Columbia University researcher, told jurors on Oct. 20 that he was "disappointed" in White for suggesting earlier that Jackson may have drunk the fatal dose of propofol.
Shafer's dismissive comment that even first-year medical students knew that wouldn't work cut deeply for White, who worked on propofol for six years before it was approved for use in the United States.
As Shafer testified, White occasionally shook his head until being admonished by a judge to stop making any gestures in court.
White, according to a report posted online by E! Entertainment Television, turned to reporters while Shafer testified and called either Shafer or a prosecutor a "scumbag." White later told a judge he didn't recall making the remark but acknowledged talking to an E! reporter about being bothered by Shafer's testimony.
"Of course, when someone makes derogatory comments about you in court, it has an effect on you," White told the judge. "I was very disappointed in Dr. Shafer's remark."
White's interview may earn him a contempt-of-court violation for violating a gag order, but that issue will be decided after Murray's trial is concluded.
The courtroom rhetoric between the men cooled last week, with White repeatedly crediting Shafer for his work.
"Dr. Shafer is actually a good friend, and he actually helped me on a number of the papers," White testified.
White left behind any hurt feelings as he took the witness stand and matter-of-factly detailed his theory that Jackson must have given himself a fatal dose of propofol. It was the only explanation, White said, for the levels of the drug found in Jackson's blood and urine during an autopsy.
Shafer wasn't in the courtroom when White testified but may be called as a rebuttal witness. Prosecutors will begin their cross-examination of White on Monday.
Shafer previously ruled out the self-administration theory, calling it "crazy" and saying Jackson would have been too groggy to pull it off. For emphasis, he placed the theory on a chart and crossed it out with a big red "X." He told jurors the only explanation for Jackson's death was that Murray placed the singer on an IV propofol drip and left the room when he appeared to be sleeping comfortably.
Shafer said Murray committed 17 egregious violations of the standard of care and should have never been giving the singer propofol as a sleep aid.
"We are in pharmacological never-never land here, something that was done to Michael Jackson and no one else in history to my knowledge," he told jurors.
White's testimony did not address Murray's conduct.
The differing viewpoints are understandable, given the lack of information the men have to make their conclusions, said Dr. Zeev Kain, chairman of the anesthesiology department at the University of California, Irvine.
"I was a bit surprised at how much was unknown," Kain said. "When all you have are blood levels in certain body parts and that is it, it is very hard to come up with a theory of what happened. I think that explains the different opinions."
Shafer and White both considered Murray's statement to police two days after Jackson's death and the autopsy results that showed the singer died with propofol throughout his body. The drug metabolizes quickly and is usually gone from the bloodstream within 10 minutes.
Murray kept no medical records of his treatments of Jackson.
Kain said it's not every day that anesthesiologists have such a high-profile stage to discuss their craft, and both White and Shafer have represented the field well.
Murray's case, through the testimony of two respected colleagues, should give the public a better understanding of anesthesiology, Kain said.
Jurors will undoubtedly have a better understanding of the drug when they begin deliberations later this week. Which of the professors' theories they believe caused Jackson's death could seal Murray's fate.