The Los Angeles coroner has ruled that Michael Jackson's death was homicide, while police have found evidence pointing to manslaughter during a search of a clinic used by his doctor.
The coroner confirmed Jackson had lethal levels of the powerful anaesthetic propofol in his body.
Court documents unsealed in Houston, Texas, revealed that Dr Conrad Murray had admitted to detectives that he gave the singer several different drugs in the hours before the star died, after he repeatedly complained of insomnia.
These included propofol, a powerful anesthetic usually only used in surgery, which the coroner said had been found in high levels in the body of the "King of Pop".
Forensic tests reportedly showed that propofol, acting together with at least two sedatives, to cause his death.
The coroner's findings increase the likelihood that Dr Murray will face criminal charges, police in Los Angeles said.
The cardiologist was reportedly offered $150,000 a month to look after Jackson. He was with the singer at his rented Los Angeles mansion on the morning of his death.
Under Californian law, a homicide does not have to be intentional killing and investigators are understood to be looking at whether the doctor's decision to give propofol to Jackson outside a hospital environment constituted a level of negligence required for an involuntary manslaughter charge.
Since Jackson, 50, suffered cardiac arrest and died on June 25, police have searched Dr Murray's home and his two clinics in Las Vegas and Houston.
According to a search warrant affidavit, Dr Murray told police he had been treating the singer for insomnia for around six weeks and had administered several drugs, including propofol. He claimed Jackson had already been given it by other doctors and referred to the drug as his "milk".
Dr Murray told investigators that he feared that Jackson was becoming addicted to the drug and halved his dosage from 50 milligrams a night to 25 milligrams, administering the drug via an intravenous drip.
On the morning he died, Dr Murray said he gave Jackson a cocktail of drugs, starting with valium at 1.30am, an intravenous injection of lorazepam half an hour later and, when the singer was still awake at 3am, some midazolam.
After giving various drugs over the next few hours, Dr Murray told officers he finally gave in to Jackson's repeated demands for propofol and administered 25 milligrams.
Returning from making phone calls to find his patient not breathing, he told police he tried to resuscitate him and one of Jackon's staff called for an ambulance. Jackson was later declared dead at hospital.
Dr Murray's lawyer has previously said he never administered anything that "should have" killed Jackson.