Alberto Alvarez, one of Michael Jackson's security guards, testifies during Dr. Conrad Murray's trial in the death of pop star Michael Jackson in Los Angeles September 29, 2011.[Photo/Agencies]

A former bodyguard for Michael Jackson testified on Thursday that the pop star's doctor asked him to grab vials of medicine and an IV bag before an ambulance was called for Jackson the day he died.

Witnesses on the third day of the involuntary manslaughter trial of Dr. Conrad Murray over Jackson's 2009 death described a chaotic scene at the singer's mansion that day, and attorneys for the physician challenged their recollections.

Prosecutors say Murray, who has admitted to giving Jackson the powerful anesthetic propofol that morning as a sleep aid, had discovered Jackson was not breathing at around 11:56 a.m.

Jackson's personal chef described Murray running frantically down the stairs at the singer's Los Angeles mansion between 12:05 p.m. and 12:10 p.m. on June 25, 2009.

"His energy was very nervous and frantic and he was shouting, 'Get help, get security, get (Jackson's then 12 year-old son) Prince'," chef Kai Chase testified.

Bodyguard Alberto Alvarez was one of the first members of the household to arrive in Jackson's bedroom.

"While I was standing at the foot of the bed, he (Murray) reached over and grabbed a handful of vials and then he said 'Here put them in a bag'," Alvarez testified.

Alvarez said Murray then pointed toward an IV stand by Jackson's bed and told him to grab one of the saline bags hanging there and take it away.

The bag had "what appeared to me like a milky white substance. I recall seeing it at the bottom of the (saline) bag," Alvarez said.

MILKY SUBSTANCE

Prosecutors say the milky substance was propofol, which authorities deemed to be the main cause of Jackson's death.

Prosecutors have suggested Murray was trying to cover up evidence of the drugs he had given Jackson by having them bagged up, and not immediately calling for an ambulance.

But Murray's defense attorney, Ed Chernoff, questioned Alvarez's memory of that day.

"Can you think of any reasons why Dr. Murray would conspire with you to hide evidence," Chernoff asked Alvarez, after the guard had admitted that he did not know Murray well.

Alvarez did not get a chance to answer because prosecutors objected and the judge squashed the inquiry.

Chernoff also grilled Alvarez about how, according to his testimony, he could have found the time within a minute or less of walking into Jackson's bedroom to usher the children out the door, bag up the drugs and take down an IV bag, before calling for an ambulance at 12:20 p.m.

"I'm very efficient, sir," Alvarez said, to chuckles in the courtroom.

Asked why he complied with Murray's request to remove the bag and vials of medicine, Alvarez told the court, "I thought we were packing to get him ready to go to the hospital."

Chase, the chef, was grilled by defense attorneys about why, when Murray asked her to get help, she first went to get Jackson's son Prince.

"I want to ask you why you did not get security?" said attorney J. Michael Flanagan.

"Because at the time what I saw was a human being (Prince) in front of me and that was the best choice I could make," Chase said.

Murray's defense team has argued that Jackson gave himself sedatives and extra propofol when the doctor was out of the room, and the additional dose killed him.

Murray faces up to four years in prison if convicted of involuntary manslaughter.