Houston, Texas (CNN) -- Michael Jackson's last physician, Dr. Conrad Murray, wasn't the one who gave the pop star a fatal overdose of propofol, according to Murray's attorney, hinting at the defense strategy in the involuntary manslaughter case against his client.
"The fact (of the way) that he died was a mystery a year ago, and still is," Houston attorney Ed Chernoff told CNN in an exclusive interview recently.
The Los Angeles County coroner ruled that Jackson's June 25, 2009, death was from an overdose of propofol, a powerful anesthesia used to put surgical patients to sleep.
Murray is charged with involuntary manslaughter in Jackson's death. His preliminary hearing is expected this fall.
Murray, hired as Jackson's personal doctor while he rehearsed for his comeback concerts, admits he was giving Jackson propofol as a sleep aid, but Chernoff said the amount was much smaller than what was found in Jackson's body during the autopsy.
The toxicology results included in the autopsy report said the propofol level was equal to what would be used to sedate a patient for major surgery.
"There is no way that Dr. Murray pumped Michael Jackson full of propofol sufficient for major surgery," Chernoff said. "No way. I would stake anything that I own on this fact."
Theories of how Jackson might have gotten the fatal dose, other than from Murray, include someone else entering the upstairs bedroom and administering it -- or Jackson waking up and giving it to himself.
A anesthesia expert hired by the coroner addressed the possibility that Jackson may have accidentally killed himself with propofol.
"It would have been difficult for the patient to administer the drugs to himself, given the configuration of the IV set-up," the expert wrote in the autopsy report.
Chernoff said the possibility was not completely ruled out by the expert.
"The coroner's report deemed it to be unlikely, because it would be difficult, so I'm assuming they've addressed that situation and that's what they believe, but is it possible? Absolutely, it's possible," Chernoff said.
Jackson's personal doctor
Chernoff said Murray had no idea what he was getting into when he signed on as Jackson's personal physician. Murray was reluctant to accept the job despite the $150,000 monthly salary, Chernoff said.
"He was leaving two practices, one in Houston and one in Nevada," Chernoff said. "He was going to be giving up those practices that he built up over 20 years, with no guarantee that when he was done with Michael Jackson he would have his practices back."
Murray knew Jackson had trouble sleeping, but did not know he was using propofol as a sleep aid, Chernoff said.
"Did Dr. Murray know that 'when I get onboard treating Michael Jackson that I'm going to have to deal with this drug propofol?' No," Chernoff said.
Chernoff said Murray was trying to wean Jackson off an addiction to propofol.
"He wanted to help him do that," Chernoff said. "Who else is addicted to a drug like propofol?"
The anesthesia expert consulted in the autopsy report said propofol was intended for use only in a surgical setting.
But Chernoff defended Murray's usage of the drug in a residential setting.
"The fact that medicines may have been prescribed or administered at home -- that alone doesn't make it egregious," he said. "A hospital is just four walls. I can't say he was in over his head, but he certainly was intending to try to help Jackson get off that drug."
The hours before Jackson died
Murray told investigators that he tried for nine hours to get Jackson to sleep the day he died, starting at 1:30 a.m. By 10:40 a.m., after giving Jackson several other sleep aids, Murray said he gave Jackson 25 milligrams of propofol through an intravenous tube attached to Jackson's leg.
The doctor's whereabouts during the 90 minutes leading up to when Jackson was found unresponsive are unclear. Phone records show Murray made three calls totaling 47 minutes during that time.
Murray told investigators he left Jackson's side for "two minutes maximum" while he went to use the bathroom, according to a police affidavit filed in the case. The timing is important because it's the only window when someone else, including Jackson, could have administered the fatal dose of propofol.
Prosecutors said the evidence points toward Murray as the only person responsible for Jackson's death.
Chernoff said he's confident that a jury will see it differently.
"We get a fair jury and we are able to afford just some of the necessary experts and investigators then, yes, the doctor is going to win," he said.
"Whatever the doctor did for Michael Jackson, whatever he did, was to help, and he took the necessary precautions and then something happened that is unexplainable," Chernoff said.