Michael Jackson's bodyguard is due to give evidence against the doctor who allegedly gave the superstar a lethal drugs dose before he died.
Prosecutors say Dr Conrad Murray ordered the bodyguard to conceal syringes and other items before calling the emergency services.
The doctor is facing a preliminary hearing in Los Angeles to determine whether he should be tried for involuntary manslaughter.
Alberto Alvarez is expected to shed light on the chaotic efforts that failed to revive the King of Pop on June 25, 2009.
The bodyguard's testimony could provide key corroboration to the prosecutors' argument that Murray's actions demonstrated "an extreme deviation from the standard of care" by administering the powerful anaesthetic propofol without the proper equipment, and also concealing it and botching efforts to resuscitate the singer.
An autopsy report found Jackson died from an overdose of propofol.
Deputy District Attorney David Walgren said that Murray forced Alvarez, 34, to gather and conceal items before calling the emergency number 911 to try to help Jackson. Walgren told a judge that he would present evidence that Murray waited as much as 21 minutes before calling for paramedics.
At the end of the preliminary hearing, which was expected to go into next week, a judge will rule whether there is enough evidence for Murray to stand trial on an involuntary manslaughter charge over the pop star's death. He faces up to four years in prison if convicted.
The Houston, Texas, cardiologist has pleaded not guilty, and his lawyers have contended he did not give Jackson anything that "should have" killed the singer.
Another bodyguard, Faheem Muhammad, testified that he saw Jackson lying on his bed, his eyes and mouth wide open, when he arrived. He described Murray as panicked, and that the doctor asked whether anyone knew CPR.