Murray has emerged as the central figure in the mystery surrounding Jackson's death in Los Angeles on June 25 and was the last person to have seen the tragic pop star alive.
The official coroner's report into the 50-year-old singer's demise has deferred the cause of death, amid speculation that powerful prescription drugs he was believed to be taking may have been to blame.
Suspicion has also focused on a dangerous sedative -- Diprivan -- used to induce unconsciousness in hospital patients ahead of major surgery, which reports say was also found in Jackson's home.
Television reports showed several law enforcement agents entering Murray's offices in Houston in a dramatic new twist to the four-week-old investigation into Jackson's death.
A spokeswoman for Murray's legal team said Wednesday's raid had come as a surprise.
"No-one told us, the DEA didn't tell us, LAPD didn't tell us. Last thing we knew we scheduled a third interview and then this happened. This is unexpected, let's just put it like that," Miranda Sevcik told AFP.
Murray's lawyer Ed Chernoff later confirmed in a statement that the search warrant served by investigators had been seeking evidence of manslaughter.
"We can confirm that a search warrant was executed today on Dr. Murray's offices in Houston Texas," Chernoff said.
"The search warrant authorized law enforcement to search for and seize items, including documents, they believed constituted evidence of the offense of manslaughter."
The wording of the search warrant provided the clearest indication yet that authorities are viewing Jackson's death as a criminal matter.
Los Angeles police had previously refused to rule out homicide in the case but had shied away from making any formal announcement that Jackson's death could result in criminal charges.
In a statement issued by Murray's lawyers late Tuesday, attorneys said the doctor was anxious to assist authorities in their investigation and that a third interview was to be scheduled.
"The coroner wants to clear up the cause of death, we share that goal," Chernoff said. "We don't have access to the most important information in this case... the toxicology report. We're still in the dark like everybody else."
Murray is currently in Las Vegas, his legal team said and Chernoff insisted that "based on Dr. Murray's minute-by-minute and item-by-item description of Michael Jackson's last days, he should not be a target of criminal charges.
"Dr. Murray was the last doctor standing when Michael Jackson died and it seems all the fury is directed toward him," he said on the website.
"Dr. Murray is frustrated by negative and often erroneous media reports, he has to walk around 24-7 with a bodyguard. He can't operate his practice."
The Los Angeles Times said Sunday the case could be hard to prosecute, with five doctors having now been questioned.
"If it is a combination of drugs -- and these drugs... were coming from multiple sources -- the argument can be made that the doctors did not know their patient was doctor-shopping," Vesna Maras, a former Los Angeles County deputy district attorney, told the newspaper.
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