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Los Angeles (CNN) -- The anesthesiologist who testified last week that Michael Jackson probably died from drugs he gave himself returned to the court Monday to face questioning by the prosecution in the trial of Dr. Conrad Murray.

Closing arguments, followed by the start of jury deliberations, could come this week or early next week in Murray's involuntary manslaughter trial.

Los Angeles County Deputy District Attorney David Walgren was given the weekend to consult with his anesthesiology expert on how to attack the testimony of Dr. Paul White, who is the last and most important defense witness.

The prosecution contends that Murray's reckless use of the surgical anesthetic propofol to put Jackson to sleep caused Jackson's death, but the defense blames Jackson for self-administering the fatal overdose while Murray was not watching.

 

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The defense contends Jackson's insomnia, unknown to Murray, was a side effect of withdrawal from a Demerol addiction, which they blame on another doctor.

The Los Angeles County coroner ruled that Jackson's June 25, 2009, death was caused by "acute propofol intoxication" in combination with two sedatives.

Jurors must choose between two competing theories offered by White and Dr. Steven Shafer, the prosecution's anesthesiologist, of how and when the fatal overdose entered Jackson's body.

Both doctors, longtime friends and colleagues, are among the top experts in the world concerning propofol.

White, in his testimony for the defense Friday, said the level of drugs found in Jackson's stomach, blood and urine, convinced him that the pop icon died after he rapidly injected himself with propofol on top of a large dose of lorazepam he swallowed when Murray was away.

Shafer, who testified over an 11-day span for the prosecution, concluded the "only scenario" that fits the scientific evidence is that Jackson was on a constant IV drip of propofol for three hours before his death.

Shafer testified that Murray must have also injected Jackson with a series of large doses of lorazepam, a sedative, hours before his death.

The prosecution theory requires "an incredible coincidence of circumstances" using a "befuddling" IV drip configuration and an "irrational" assumption about how Murray injected sedatives, White testified.

White testified Friday that it is his opinion Jackson died after he injected himself with a 25-milligram dose of propofol between 11:30 a.m. and noon. Testimony and phone records indicated it was about noon that Murray realized Jackson was not breathing.

White theorized that Jackson could have "pushed" the drug into an catheter in his leg using a syringe over a 15- to 30-second period, much faster than a doctor would have done.

"I believe it could potentially have lethal consequences," White testified.

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

Murray is responsible for Jackson's death, even if he did not give him the final and fatal dose, because he was criminally reckless in using the surgical anesthetic to help Jackson sleep without proper precautions, the prosecution contends.

While Jackson was hooked up to an IV drip, it only delivered a saline solution to keep him hydrated, the defense contends.

Shafer demonstrated in court how he believed the IV system was set up by Murray, but investigators never found a critical piece of tubing that would have been needed to infuse a propofol drip into the catheter in Jackson's left leg.

The 100-milliliter propofol bottle prosecutors believe Murray used was empty when investigators found it, leading Shafer to conclude that the last drops entered Jackson's body just as his heart stopped beating.

White called it "an incredible coincidence of circumstances" that the bottle would empty exactly when Jackson died.

White also said such a flow of propofol would have made Jackson "sleepy but arousable and breathing spontaneously," but it would not have killed him.

But Murray's own words, spoken to police two days after Jackson's death, led the jury toward Shafer's drip theory and away from White's self-injection theory.

Murray told detectives that the pulse oxymeter monitor on Jackson's finger showed his heart was beating at 122 beats per minute after he realized his patient was not breathing. This would indicate Jackson suffered respiratory arrest first, followed about 10 minutes later by cardiac arrest, a cardiologist and Shafer both testified.

The difference is key to interpreting what the high level of propofol in Jackson's blood means, since a beating heart would circulate the drug through the liver, which would break it down into a metabolite.

White's theory that Jackson died quickly from a rapid injection requires the assumption that his heart almost immediately stopped beating, before Murray would have seen the monitor on his finger.

The defense expert also questioned the prosecution's contention that Murray placed the propofol bottle into an empty saline bag with an opening cut into it to suspend it from the IV stand next to Jackson's bed.

It would have been more logical for Murray to use a plastic suspension tab built onto the bottle, a routine practice.

"It's befuddling to me, because anyone picking up the bottle would naturally gravitate for pulling up the little hanger," White said. "Why would you go to all the hassle?"

Hanging the bottle inside a bag also would not work because if Jackson "rolled over and moved his leg, it would easily come out of the bag," White said.

The suspension tab on the propofol bottle had not been activated, both sides agreed.

Investigators who recovered the bottle and an opened bag testified they found them together, but they did not photograph it.

White also questioned Shafer's computer model conclusion that Murray gave Jackson at least nine four-milligram injections of the lorazepam at regular intervals from 1:30 to 5 a.m. the day he died.

Those "enormous" sedative doses alone would have put anyone to sleep and possibly killed them, White said.

He said it would be "irrational" for a doctor to sit at Jackson's bedside and repeatedly inject the sedatives to a patient in very deep sedation, as Shafer's theory implies.

White concluded that Jackson swallowed a large dose of lorazepam several hours earlier, which would have left "a very high concentration" of the sedative in his body.

"So you've got drugs that have additive or even synergistic effects, and I think the combination effect would be very profound," White said.