Michael Jackson’s death has been ruled a homicide, the Los Angeles County Coroner confirmed last night in a decision that could lead to criminal charges being brought.

A release from the coroner’s office confirmed suggestions made this week that the singer’s death had been caused by “acute propofol intoxication” following lethal levels of the powerful sedative.

Court documents disclosed that Jackson’s doctor, Conrad Murray, 51, had administered propofol along with a number of other sedative drugs in the hours before the singer collapsed at his rented home in Los Angeles.

Dr Murray has not been named as a suspect in the investigation. Under US law the homicide ruling could refer to murder or negligent or reckless manslaughter, opening the possibility that criminal charges will be brought if someone is found to be to blame for Jackson’s death.

The coroner’s report stated that the presence of the drug benzodiazepine contributed to Jackson’s death, though coroners also found diazepine and ephedrine in his system. Documents released by a court in Houston on Monday revealed that Jackson had been given a cocktail of sedatives to help him sleep. Dr Murray told police that he feared Jackson was developing an addiction to propofol and so had been decreasing the dosage that he administered.

Dr Murray said that on the morning of Jackson’s death he had given him valium at 1.30am and then injected lorazepam intravenously at 2am. An hour later Jackson was still awake and Dr Murray gave him midazolam.

At around 10.40am Jackson reportedly demanded to be given propofol. Dr Murray said that he gave a reduced dosage after trying to induce sleep with other drugs.

Court reports suggested that the doctor left Jackson’s side soon after admistering the drug but Dr Murray has denied this claim. Since the investigation began, Dr Murray has been interviewed on two occasions by police, who have also searched two offices and a pharmacy connected with the physician.

Court records have identified the doctor as the subject of a manslaughter investigation and officials from the Drug Enforcement Administration have been involved in establishing where he obtained the propofol that he administered to Jackson.

Last week Dr Murray posted a video on YouTube in which he defended himself against the increasing suspicion against him. He said: “I have done all I can do. I told the truth, and I have faith the truth will prevail."

Jackson’s dermatologist, Arnold Klein, is also facing police scrutiny. Dr Klein has admitted giving the singer demerol, a painkiller.

The investigation reportedly includes enquiries with doctors in Germany who may also have given the singer drugs to help him to sleep.

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