Murray, a Texas-based cardiologist, allegedly gave Jackson the anesthetic propofol -- commonly known by the brand name Diprivan -- in the 24 hours before he died, the source said.
The doctor's attorneys in a statement Monday said they wouldn't comment on "rumors, innuendo or unnamed sources." In the past they have said Murray never prescribed or administered anything that could have killed the pop star.
Last week, Texas authorities searched Murray's Houston medical office and storage unit, looking for "evidence of the offense of manslaughter," according to court documents.
Among the items removed from Murray's office were a computer; 27 tablets of phentermine, a prescription-strength appetite suppressant; 1 tablet of clonazepam, an anti-anxiety medication; and some Rolodex cards.
From Murray's storage unit, authorities removed two computer hard drives; and "important contact list;" a suspension notice from Houston's Doctor Hospital; notices from the Internal Revenue Service; and a laundry list of medical and hospital documents.
Ed Chernoff, a Houston lawyer hired by Murray soon after Jackson's death, confirmed at the time that Los Angeles Police detectives and federal Drug Enforcement Administration agents used a search warrant to enter Murray's office in northeast Houston Wednesday morning.
Chernoff said members of Murray's legal team were at the medical office during the search, which he said "was conducted by members of the DEA, two robbery-homicide detectives from the Los Angeles Police Department and Houston Police officers."
Tammy Kidd, a spokeswoman at Chernoff's office, told CNN the search "was absolutely a surprise to us, because we've had open lines of communication this whole time."
Police have interviewed Murray twice since Jackson's death. A third interview was scheduled for July 24, but was postponed after the search warrants were executed. It's unknown when the next interview will take place.
Among those who have indicated that Jackson may have been using dangerous prescription medication are a nutritionist -- Cherilyn Lee -- who said Jackson pleaded for the powerful sedative Diprivan despite being told of its harmful effects.
Meanwhile, the Los Angeles County coroner's office continues to investigate the cause of Jackson's death on June 25. It has been waiting on toxicology lab results, but a final autopsy report is expected as soon as this week, a coroner's spokesman has said.
--CNN's Ted Rowlands contributed to this report.
TM & © 2009 Cable News Network, Inc., a Time Warner Company. All rights reserved.