Police who searched Michael Jackson's home the day after he died were acting on information from family members who said they'd found a bag of heroin in his bedroom, but a person with knowledge of subsequent test results on the substance said it turned out not to be the drug.

The search did, however, turn up a number of other drugs including marijuana, the generic form of Valium and other sedatives. A detective also indicated Jackson's body showed signs of injections.

The disclosure came in an affidavit supporting a search warrant that was executed on June 26, three days earlier than any previously reported search of Jackson's rented mansion in Bel-Air.

Two warrants came to light after several media outlets asked to unseal four search warrants Los Angeles police detectives served in the early days of the Jackson death probe. The judge ordered two of the documents to remain sealed.

The unsealed warrants provide a glimpse into how police were directing their investigation immediately after Jackson's death.

The warrant served at his rented Bel-Air mansion the day after he died lists PC 187, the California penal code for murder, in the box labelled "probable crime".

That warrant states family members told a coroner's official "they had located a quantity of tar heroin in a bag in the decedent's bedroom," though the person with knowledge of tests on the substance said heroin was quickly ruled out.

Detectives also secured a search warrant for the car of Dr Conrad Murray, the personal physician with Jackson when he died.

The affidavit states detectives spoke to Dr Murray in the hospital after the singer's death but he only gave a short summary of what had happened then left the hospital over detectives' objections.

In the intervening two months, investigators have pieced together a much fuller picture of how Jackson died and Dr Murray has emerged as the central figure in a manslaughter probe.

Investigators believe he was negligent in administering the powerful anaesthetic propofol and other sedatives to Jackson and that those drugs killed the singer.

Dr Murray's attorney Edward Chernoff has said Murray never administered anything that "should have" killed Jackson.

The coroner has not officially released autopsy results but reports say the death has been ruled a homicide.

The search of Dr Murray's car turned up some documents, but no additional drugs.