Houston , Texas ( CNN ) -- Michael Jackson 's last physician , Dr. Conrad Murray , was n'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 does n't make it egregious , '' he said . `` A hospital is just four walls . I ca n'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 .
Lawyer : Dr. Murray did not cause Jackson fatal overdose . Murray was given propofol to help Jackson sleep . Sheriff : Someone else may have caused Jackson 's death . Autopsy report said it is unlikely Jackson injected himself .