Just three detectives are investigating the death of Michael Jackson.

Key witnesses – including the 'Thriller' star's chief of staff Michael Amir and his security officer Alberto Alvarez - have not yet been interviewed because Los Angeles police are so busy.

Carl Douglas, a lawyer for both staff members, said: "We arranged two occasions for investigators to meet my clients.

"The first meeting was rescheduled. The second, I had to call them to inquire about the detectives' absence."

Alberto – who alerted emergency services when Michael was discovered unconscious on June 25 - in particular is considered crucial to the investigation into establishing what happened after the star's doctor, Conrad Murray, injected him with the powerful anaesthetic Propofol.

A source said: "There are only three detectives from LAPD's homicide division assigned to the case.

"This is one of the reasons the investigation is ongoing."

Meanwhile, marijuana and several empty drug bottles were found by police at the 'Billie Jean' star's home shortly after he died.

Two bags of the herbal drug, a bottle of sleeping medication Temazepam, empty packaging for sedatives Lorazepam and Diazepam and four unlabelled vials were uncovered during a search of the property, search warrants unsealed yesterday (27.08.09) have revealed.

The search warrants also discovered that officers were tipped off about the singer's drug stash by family members who had discovered 'tar heroin'.

The documents read: "During the course of the investigation, family members of the decedent notified L.A. County Coroner's Assistant Chief Winter that they had located a quantity of tar heroin in a bag in the decedent's bedroom located on the 2nd floor. Chief Winter notified LAPD detectives of the found evidence"

There is no mention in the warrant if the evidence turned out to be heroin, but it is believed to have been marijuana.

Meanwhile, website Entertainment Tonight has claimed the Los Angeles County Coroner's office will announce the cause and manner of Michael Jackson's death today (28.08.09).

The website says a statement will be issued on the matter, rather than a press conference being called.