Federal agents and detectives swooped on the offices of Michael Jackson's doctor on Wednesday as lawyers for the physician revealed police are treating the star's death as possible manslaughter.
A spokeswoman for the Drug Enforcement Administration (DEA) confirmed that a search with the Los Angeles police took place at the offices of the Armstrong medical clinic in Houston, Texas, where doctor Conrad Murray practices.
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 at his mansion.
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 or propofol - 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.
Murray's lawyer Ed Chernoff 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 on Thursday 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 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 on late Tuesday, Chernoff said Murray was anxious to assist authorities in their investigation and that a third meeting with police was to be scheduled after two earlier interviews.
"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."
In the immediate aftermath of Jackson's death friends of the singer's family said the clan was unhappy with "unanswered questions" surrounding Murray.
"They (the family) are suspicious of this doctor and they have real reason to be because any other doctor would say 'Here's what happened in the last hour of his life and I was there. I gave him some medicine,'" family friend Jesse Jackson said.
"(Murray) owes it to the family and to the public to say, 'These were the last hours of Michael's life and here's what happened.' That's a reasonable expectation."
The Los Angeles Times said on Sunday any manslaughter 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.