LOS ANGELES - As Michael Jackson's lifeless body lay on a bed in his palatial mansion, a bodyguard obeyed a frantic doctor's instructions to bag up medicine bottles and intravenous bags and shield the Jackson children from seeing their father - all before being told to call 911, court testimony revealed Wednesday.

Alberto Alvarez said he was the first security guard to reach Jackson's room after word came that something was wrong. He described a shocking scene.

The King of Pop was on his bed connected to an IV tube and a urinary catheter. His eyes and mouth were open, and Dr. Conrad Murray was leaning over him doing one-handed chest compressions to try to revive him.

Alvarez said he was "frozen" at the sight.

"I said, 'Dr. Murray, what happened?' And he said, 'He had a reaction. He had a bad reaction,'" Alvarez recalled.

The testimony came during a preliminary hearing to determine if Murray, the singer's personal physician, will be tried on a charge of involuntary manslaughter.

Authorities contend Murray gave Jackson a lethal dose of the powerful anesthetic propofol and other sedatives in the bedroom of his rented mansion before he died on June 25, 2009.

Deputy District Attorney David Walgren said in his opening statement that Jackson was already dead when Murray summoned help and tried to conceal his administering of propofol to the pop star, ordering the bodyguard to collect items before paramedics were called.

Murray was providing Jackson propofol roughly six times a week since being hired as his physician in May 2009, as Jackson prepared for a series of comeback concerts, Walgren said.

In other testimony, paramedic Richard Senneff, who responded to Jackson's mansion the day he died, said Murray never mentioned he had given propofol to the singer. Instead, the doctor said he had given Jackson lorazepam to help him sleep and indicated the pop star was being treated for dehydration, Senneff testified.

The paramedic testified that Murray's responses didn't add up, because the singer looked so pale and thin that Senneff thought he was a hospice patient.

Earlier, Alvarez recalled Jackson's children Paris and Prince walking into the room during the effort to revive their father.

"Paris screamed, 'Daddy!' and she started to cry. Dr. Murray said, 'Get them out. Don't let them see him like this,'" the bodyguard said.

Alvarez's voice choked as he described Paris crying and he took a moment to compose himself.

"I said, 'children, don't worry, we'll take care of this.' And I escorted them out and left the door ajar," Alvarez said.

In the courtroom audience, Jackson's mother, Katherine, dabbed at her eyes during the most detailed public account yet of events surrounding the death of her son. She came to court with her husband, Joe, and children Randy, Janet and LaToya. They made no eye contact with Murray across the courtroom.

They heard Alvarez testify that he helped Murray bag the medicine and saw an unidentified "white milky substance" in the bottom of an intravenous bag.

"He just grabbed a handful of bottles, or vials, and he instructed me to put them in a bag," Alvarez testified, adding that Murray also told him to place an intravenous bag into another sack.

"Is it true that 911 had not been called yet?" Walgren asked.

"That's true," Alvarez replied.

After collecting everything and bagging it, Alvarez said, Murray told him to call 911. The prosecutor then played a recording of the call.

When the operator said to transfer Jackson to the floor, Alvarez grabbed Jackson's legs and Murray grabbed his upper body. He said at that point he noticed the IV in Jackson's leg that had to be removed. Alvarez also saw that Jackson had the urinary catheter.

Alvarez said Murray then asked him to give Jackson chest compression, while Murray did mouth-to-mouth resuscitation.

Murray said, "'You know this is the first time I give mouth-to-mouth but I have to do it because he's my friend,'" Alvarez recalled.

"Did it appear he was breathing," Walgren asked.

"No sir," Alvarez said.

"His eyes and mouth were open?" the prosecutor asked.

"Yes," the witness said.

"Did he seem to be alive or dead?" Walgren asked.

"Dead, sir," Alvarez said.

In his opening statement Tuesday, Walgren said Murray had waited as long as 21 minutes before paramedics were called and that Jackson had died before help was summoned.

The testimony could support the prosecutors' argument that Murray's actions demonstrated "an extreme deviation from the standard of care" by administering propofol without the proper equipment, and also concealing it and botching efforts to resuscitate the singer.

Murray, a Houston cardiologist, has pleaded not guilty, and his attorneys have contended he did not give Jackson anything that should have killed him.

Defense lawyers did not deliver an opening statement at the hearing. Murray could face up to four years in prison if tried and convicted.

AP entertainment writer Anthony McCartney contributed to this story.