Michael Jackson's physician, Conrad Murray, right, arrives for his arraignment at the Airport Branch Courthouse in Los Angeles on Monday. (Damian Dovarganes/Associated Press)

Dr. Conrad Murray, who was caring for Michael Jackson at the time of the pop star's death, has pleaded not guilty after being charged Monday with involuntary manslaughter.

Los Angeles prosecutors announced the long-awaited charge against Murray, a cardiologist with practices in Houston and Las Vegas, early Monday.

Murray surrendered to police, appearing in a Los Angeles court in the morning, to enter his plea.

Murray was released Monday afternoon after posting bail of $75,000 US.

His lawyer said the doctor plans to return to his medical practices in Houston and Las Vegas while he awaits trial. However, state officials said they plan to ask the court to suspend Murray's medical licence while he's free on bail.

Jackson's father, Joe, his mother, Katherine, and siblings LaToya, Jermaine, Tito, Jackie and Randy sat behind prosecutors during the court appearance.

Jackson's family members have said publicly they wanted the doctor to face the more serious charge of second-degree murder.

Jackson was preparing for a string of sold-out appearances in London, England, when he died last June in Los Angeles at age 50.

Plagued by sleeplessness, he had hired Murray as a personal physician as he took on a tough schedule ahead of his comeback concerts.

Prosecutors allege he gave Jackson the powerful anesthetic propofol to help him sleep, but that instead led to his death.

Los Angeles investigators were methodical in building a case against Murray, taking six months to investigate the doctor's actions and where he obtained the drugs found in the pop star's Los Angeles home.

They may have been wary after observing the missteps in prosecuting high-profile cases like O.J. Simpson and actor Robert Blake, both of whom were acquitted of murder.

Coroner rules homicide

A coroner ruled last summer that Jackson's death was a homicide caused by acute intoxication of propofol, with other sedatives a contributing factor. However, they said he was otherwise healthy, a factor that may weigh against Murray in court.

Detectives spoke to more than 10 medical experts in the course of their investigation to see if his behaviour fell outside the boundaries of reasonable medical practice.

Court documents show Murray told police he administered the drug to the singer. He also was with Jackson when household staff called for paramedics.

Murray appears to have obtained the drug legally and its use is not in itself a crime. Part of the case may rest on what happened between the administration of the drugs and when emergency help was summoned.

Prosecutors allege Murray spent part of that time on his cellphone, making non-emergency calls.

If convicted of involuntary manslaughter, he could face a maximum of four years in prison.

With files from The Associated Press