Merchandise for Jackson's O2 residency has now gone on sale
The head of Los Angeles police has refused to rule out murder in the investigation into the death of singer Michael Jackson, two weeks ago.
Police Chief William Bratton told US news broadcaster CNN that police were awaiting toxicology results.
"Are we dealing with a homicide or are we dealing with accidental overdose... I don't have that information."
Meanwhile, Jackson's father, Joe, 79, speaking about the death on ABC News, said: "I do believe it was foul play."
Mr Jackson - who is due to attend a memorial service in the family's hometown of Gary, Indiana, later - has previously said he had "a lot of concerns" over events surrounding his son's death, and that the family "suspected foul play somewhere".
The Los Angeles coroner has said that an autopsy the day after the singer's death revealed no evidence of foul play and that toxicology test results could take weeks to come back.
A spokesman for the coroner's office said Jackson had taken "some prescription medication", without specifying which.
Mr Bratton, meanwhile, told CNN that detectives were investigating the singer's history of using prescription drugs and had spoken to a number of doctors who had treated him over the years.
"We are still awaiting corroboration from the coroner's office as to cause of death," he said.
"That is going to be very dependent on the toxicology reports that are due to come back.
"And based on those, we will have an idea of what it is we are dealing [with]."
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"So as we are standing here speaking, I can tell you I don't have that information," he told reporters.
Mr Bratton said his department was being helped by other agencies, including the Drug Enforcement Administration, on "a comprehensive set of inquiries".
"At the time of the death, with search warrants, we were able to seize a number of items from the residence where the death occurred and those will assist in the investigation," he added.
Meanwhile, guests including Jackson's father and the Reverend Al Sharpton - who spoke at the Staples Center memorial in Los Angeles on Tuesday - are expected at the service in Gary on Friday evening.
The service will be held at the Steel Yard baseball park, a few miles from the singer's childhood home.
The Jacksons moved from Gary, Indiana, in 1969
Mayor Rudy Clay said the event would be a celebration of the contribution of the Jackson family to the music industry.
The entire family moved from the town to California after The Jackson Five signed with Motown records in 1969.
The group, featuring Michael and his brothers, was formed by father Joe five years earlier.
"Michael Jackson put Gary, Indiana, on the global map and made Gary citizens proud," Mr Clay said, in a statement.
Jackson had been rehearsing for comeback shows at London's O2 arena - due to begin on Monday - before his sudden death on 25 June, at the age of 50.
Shaheen Jafargholi, who sang at Tuesday's memorial, appeared in Thriller Live
Promoters AEG have announced that official merchandise for the tour - including T-shirts, mugs, belt buckles and socks - is now available to pre-order.
Meanwhile, the makers of West End tribute show Thriller Live are taking the show on a year-long world tour.
The musical, which began as a touring show in 2006, has been appearing at London's Lyric Theatre since January.
A new production of the show will be staged in Munich, Germany, on 21 July, before travelling across Europe and on to the US.
"Since the tragic news from Los Angeles broke, we have been amazed by the reaction of the fans around the globe, and inquiries for Thriller Live to appear worldwide have been overwhelming," producer Paul Walden said.