Doctor Conrad Murray - personal physician of Michael Jackson – waited up to 21 minutes before calling 911 after the singer stopped breathing, a court was told this week.
Prosecutors made the claim during a preliminary hearing into Michael Jackson's death, which has begun in LA.
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A judge will decide over the next couple of days whether there is enough evidence to try his physician, Doctor Conrad Murray.
He faces up to four years in prison if convicted of involuntary manslaughter, a charge to which he has pleaded not guilty.
Michael fans lined the streets outside the courthouse, holding banners calling for justice.
Several members of the Jackson family, including Michael's mother Catherine, brother Jermaine, and sister LaToya were present at the hearing.
They listened as prosecutors – who claim Dr Murray's negligence in treating the star for insomnia led to his untimely death – outlined the case against him.
District attorney David Walgren told the court: "There are a number of actions displayed by Dr Murray that show an extreme deviation from the standard of care."
He further alleged that when the physician realised Michael had died, he ordered a security guard to collect drugs he had used to treat the singer, and other medical paraphernalia.
Once this was done he told the bodyguard to call an ambulance, up to 21 minutes after he noticed Michael had stopped breathing, he told the court.
Mr Walden said Dr Murray had given the Thriller singer a dose of propofol - a powerful surgical anaesthetic - on the morning of 25 June 2009, after giving him various sedatives during the night.
He also claimed that the physician did not properly perform CPR. He added that when paramedics did arrive, the doctor neglected to mention that he had given Michael propofol – the drug that the Los Angeles County coroner's office ruled was responsible for his death along with the various other sedatives found in his system.
Mr Walden said he expected Dr Murray's legal team to claim Michael had injected himself with the lethal dose.
Also speaking at the Tuesday hearing was choreographer Kenny Ortega, who said the king of pop had appeared unwell and out of shape in the days leading up to his death.
He went home early from rehearsals for the London comeback tour, Mr Ortega added.