Foul play has been ruled out in the death of Michael Jackson, after doctors completed an autopsy on the singer who died on Thursday aged 50.
But tests, including toxicology, have been ordered and determining the cause of death could take several weeks, the Los Angeles county coroner said.
Jackson's body has now been released to his family but no funeral details have yet been announced.
Entertainers, world leaders and fans have paid tribute to the star.
Singers Madonna and Justin Timberlake praised his talent, while a spokesman for Barack Obama said that the US president saw Jackson as a "music icon".
Los Angeles County coroner's spokesman Craig Harvey said police had put a security hold on Jackson's case, limiting the amount of information that can be released.
"It means that the medical examiner ordered additional testing such as toxicology and other studies," Mr Harvey said.
The tests would take between four to six weeks, at which point he anticipated being able to close the case, he said.
Jackson, who had a history of health problems, collapsed at his Los Angeles home around midday on Thursday.
A recording of the telephone call made to emergency services has been released, in which the caller said Jackson was unconscious and had stopped breathing.
His personal doctor - who witnessed his collapse - was trying to revive him, the caller said.
Across the world, people have been voicing shock and disbelief at the news of his death. In Hollywood, thousands of people filed past his star on the Walk of Fame.
A White House spokesman said US President Barack Obama considered Jackson a spectacular performer, but said he felt parts of his life were "sad and tragic".