The probe into Michael Jackson's death stepped up Friday after investigators subpoenaed medical records and a leading police officer refused to rule out homicide.
Coroners called for any records held by Jackson's many doctors to be presented, "including radiology and psychiatric records," the Los Angeles Times reported, as part of an ongoing investigation into the singer's death aged 50 on June 25.
Los Angeles police chief Bill Bratton said his department was looking into Jackson's "prescription drug history, the doctors that he's dealt with over the years.
"Are we dealing with homicide? Are we dealing with an accidental overdose? What are we dealing with? So as we are standing here speaking, I can tell you, I don't have that information," he told CNN.
The pop superstar's 79-year-old father Joe Jackson meanwhile told ABC News that he remained suspicious of the circumstances surrounding his son's death.
"I do believe it was foul play," Jackson said. "I do believe that. Yes."
The Jackson family patriarch said he "just couldn't believe what was happening" when his son was rushed into hospital late last month with an apparent cardiac arrest.
The second autopsy demanded by the family following the death of their most famous member was still yet to reveal any more answers, Joe Jackson also said.
Investigators have apparently zeroed in on a powerful sedative -- Diprivan -- discovered at Jackson's rented mansion after his death.
The drug is commonly used to induce unconsciousness in hospital patients ahead of major surgery and experts say it should only be administered by a trained anesthesiologist.
Jackson's long-time dermatologist Arnold Klein told CNN earlier this week that he had been aware the singer had used the drug in the past.
"I knew at one point he was using Diprivan when he was on tour in Germany," he said. "He was using it with an anesthesiologist to go to sleep at night and I told him he was absolutely insane."
But he denied earlier being the source of the drugs. "I didn't give him this crap that they're talking about," he told ABC television in an earlier interview. "How am I going to prescribe Diprivan when I don't understand how to use it?"
Klein, who said he treated Jackson three days before his mysterious death, suggested that any doctor found to have supplied the star with drugs should be prosecuted.
Reports have also emerged of police records that include allegations Jackson used Xanax -- another powerful sedative -- and at one time took as many 30 pills each night.
Meanwhile, the mystery surrounding Jackson's final resting place deepened on the eve of a memorial service expected to be attended by family members in his hometown of Gary, Indiana.
The city's mayor announced it would hold a memorial service Friday for its most famous son, to be attended by Jackson's father Joe, fuelling speculation about where the "King of Pop" was to be buried, or if he had already been interred after Tuesday's star-studded memorial.
The star's gold-plated coffin took centre stage at a Staples Centre send off in Los Angeles on Tuesday, but there has so far been no confirmation about if and where the star was already buried.
Nielsen, a TV ratings group, said 31.1 million Americans tuned in for the event in which Jackson's daughter Paris, 11, grabbed international attention with a heartbreaking eulogy to her father.
"Ever since I was born, Daddy has been the best father you could ever imagine. And I just wanted to say I love him so much," Paris said.
Since the event, rumours have swirled that the pop icon was interred at the Forest Lawn Cemetery in Hollywood Hills, with celebrity news website TMZ.com claiming those reports were not true.
The Los Angeles Times said the body was in safekeeping and no final decision had been made about a burial time or place.
The uncertainty over Jackson's final resting place spurred rumours that his remains may yet end up at his beloved Neverland Ranch northwest of Los Angeles.
Jackson sold more than 750 million albums during a four-decade career that was tainted by child abuse allegations, his startling physical transformation and eccentric behaviour.
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