But in a sidebar session, it was a prospective witness for Murray's defense under attack, being excoriated by Judge Michael Pastor for apparently denouncing either a prosecution witness or a prosecutor as a "scumbag" within earshot of reporters, possibly in contempt of court.
Murray is on trial in Los Angeles Superior Court for involuntary manslaughter involving Jackson's death.
The prosecution witness, Dr. Steven Shafer, an anesthesiologist affiliated with Columbia University, has testified in recent days that Murray most likely hooked up Jackson to an IV drip containing the anesthetic propofol and then left the singer unattended.
Shafer added today that even if Jackson were able to start the IV drip on his own, Murray still would be responsible for the death.
"If Michael Jackson had reached up, seeing the roller clamp, and opened [it] himself, this is a foreseeable consequence of setting up a dangerous way of giving drug [and] is in no way exculpatory for the fact that Dr. Murray was not present and permitted this to happen," Shafer said.
But then the defense took its shots, questioning whether Shafer was using medical knowledge or actually doing investigative work beyond his expertise when he came up with his theory on Jackson's death.
"Everything you said in the last two days was your opinion," defense attorney Ed Chernoff told Shafer at one point. "You do understand that, right? Do you understand that?"
Answered Shafer, "I stated my name, which I think is a matter of fact."
Shafer's theory relied on Murray using a vented IV -- which would let air into the propofol bottle, allowing it to drip.
However, Chernoff noted, there was no such vented IV line found in the bedroom where Jackson was discovered unconscious.
Shafer maintained that Seacoast Medical records showed Murray had ordered vented IV's in the past, and that the IV tubing was small enough that it could have been easily removed from the room.
Later, Chernoff pressed Shafer for the corroborating evidence he used to come up with his theory that Murray put a propofol bottle in a cut-open saline bag to set up a propofol drip -- a set-up that Shafer admitted he had never seen before.
Chernoff got Shafer to concede that he relied on an earlier witness, Alberto Alvarez, who said he had seen such a set-up before stashing it in a blue bag.
The defense has attacked Alvarez's credibility on the claim he handled the IV bag because there were no fingerprints.
After Murray's defense concludes its cross-examination of Shafer next week, the prosecution is expected to rest its case and let the defense present its case.
But a prospective defense witness already faced heat today over his alleged statements, published by E! online, in possible violation of a gag order.
As Shafer demonstrated Thursday how Murray could have administered propofol to Jackson, E! reported, Murray could be heard whispering loudly to the possible witness, Dr. Paul White, "Can you believe that?" At which point, according to E!, White turned to journalists and said, "What a scumbag."
It was unclear whether White was referring to Shafer or prosecutor David Walgren.
Possible Conrad Murray Defense Witness in Contempt of Court?
But today, outside of the presence of jurors, Judge Pastor set a Nov. 16 hearing to determine whether White should be held in contempt of court.
In addition to his complaint about the "scumbag" remark, Walgren complained to the judge that White has been caught on TV cameras reacting to testimony -- "the rolling of the eyes and facial expressions, things of that nature," Walgren said, according to a transcript.
White and other medical experts have been allowed to attend court sessions to inform their possible testimony, but without publicly commenting.
"I don't want to harm Dr. Murray or defense counsel in this case by excluding Dr. White at this juncture if defense counsel still want him here," Pastor said in the transcript, "because I have to balance my concern about decorum with the defendant's right to a fair trial. But this may very well constitute a violation of the court's order."
"I'm going to talk to him," replied Chernoff, the defense attorney. "I'm embarrassed by this. You should hold me personally responsible."
Later, though, Pastor himself focused his anger on White in another sidebar session.
White said he could not recall his "scumbag" comment, but recalled making other statements to reporters and to Walgren, according to a transcript.
"You have no business making any of those comments, Dr. White," Pastor told him, "either to Mr. Walgren or in this courtroom where such comments can be overheard. This raises the issue of whether those comments constitute a violation of my continuing orders in this case, repeated on innumerable occasions.
"If you want to retain counsel, that is your absolute right, and anybody else who wants to be heard," Pastor added. "But I'm going to set it for further proceedings to determine if I should sanction you or even cite you for contempt of court."
ABC News Radio and The Associated Press contributed to this report.