Los Angeles, California (CNN) -- Dr. Conrad Murray, personal physician to Michael Jackson, has been charged with involuntary manslaughter in connection with the pop star's death last summer.

A criminal complaint filed earlier Monday alleged that Murray "did unlawfully, and without malice, kill Michael Joseph Jackson."

Murray turned himself in shortly before 4 p.m. at a branch courthouse near Los Angeles International Airport. He pleaded not guilty during a hearing before Judge Keith L. Schwartz.

Members of Jackson's family, including his parents, Joe and Katherine and three of his brothers, had arrived at the courthouse before Murray. Asked for his reaction to the charge, brother Jermaine Jackson said, "Not enough."

The involuntary manslaughter charge means that Murray caused Jackson's death by acting "without due caution and circumspection."

If convicted, Murray would face a maximum four-year prison sentence, according to prosecutors.
Deputy District Attorney David Walgren will lead the prosecution.

Murray traveled to Los Angeles at the end of January from his home in Houston, Texas, in expectation of possible charges, his lawyer said.

He used part of his time last week to visit the pop star's resting place in the Forest Lawn Memorial Park in Glendale, California.

Murray, a cardiologist, was hired as Jackson's personal physician last spring as the singer prepared for comeback concerts in London, England.

The doctor told Los Angeles police that he was with Jackson at his $100,000-a-month rented Holmby Hills mansion through the early morning hours of June 25, 2009, in an effort to help the pop star fall asleep, according to a police affidavit.

He administered sleep aids, and after Jackson finally began sleeping in the late morning hours, Murray said, he left the bedroom for "about two minutes maximum," the affidavit says.

"Upon his return, Murray noticed that Jackson was no longer breathing," it says.

The doctor stayed with Jackson as an ambulance rushed him to UCLA Medical Center.

Efforts at CPR proved fruitless, and Jackson was pronounced dead at 2:26 p.m.

The Los Angeles County coroner ruled Jackson's death a homicide, resulting from a combination of drugs, primarily propofol and lorazepam.

The coroner's statement said Jackson died from "acute propofol intoxication," but there were "other conditions contributing to death: benzodiazepine effect." Lorazepam and two other drugs Murray said he used are benzodiazepines.

The doctor told investigators he had given Jackson three anti-anxiety drugs to help him sleep in the hours before he stopped breathing, a police affidavit said.

Murray had been treating Jackson for insomnia for six weeks at the time of the singer's death. The doctor told investigators he gave Jackson 50 milligrams of propofol, the generic name for Diprivan, diluted with the anesthetic lidocaine every night via an intravenous drip.

The doctor told police he was worried that Jackson was becoming addicted to the drug and tried to wean him off it.

During the two nights before Jackson's death, Murray said, he put together combinations of other drugs that succeeded in helping Jackson sleep.