Los Angeles (CNN) -- The emergency room doctor who declared Michael Jackson dead testified Monday in the involuntary manslaughter trial of Dr. Conrad Murray that there was no way doctors could have revived the pop icon after he arrived at the hospital.
Dr. Richelle Cooper testified Friday that Murray never told her that he had given Jackson the surgical anesthetic propofol before he stopped breathing, but she said Monday it would not have made a difference if he had because Jackson "had died long before."
"It is unlikely with that information that I would have been able to do something different that would have changed the outcome," Cooper said.
Prosecutors argue that Murray's failure to tell paramedics and doctors trying to resuscitate Jackson about the propofol is one of the negligent acts that make him criminally responsible for Jackson's death.
Another doctor testified Monday that the decision to place an aortic balloon pump in Jackson's heart was "a desperate attempt, even though very much futile" effort intended "to prepare Dr. Murray mentally to accept the fact that Mr. Jackson could not be rescued and would allow Mr. Jackson to depart in peace and dignity."
Dr. Thao Nguyen said Murray asked that "we not to give up easily and try to save Mr. Michael Jackson's life," Nguyen said, even though it seemed hopeless.
They placed a balloon pump in Jackson's aorta in an unsuccessful effort to restart his heart, she said. "It's not a case of too little, too late, but a case of too late," Nguyen said.
Monday was the fifth day of testimony in Murray's involuntary manslaughter trial, which is expected to last at least four more weeks.
The trial resumed without Jackson's mother. Katherine Jackson left Los Angeles for Canada with her son's three children during the weekend to attend Sunday's premiere of Cirque du Soleil's "Michael Jackson: The Immortal World Tour" in Montreal. A source close to the Jackson family said she would not return to the trial at least until October 10, since she will also travel to Cardiff, Wales, for a tribute concert for her late son.
Jackson family members in court Monday morning included siblings Janet, Rebe, Randy and Jermaine.
Prosecutors argue that Murray, who was Jackson's personal physician as he prepared for planned comeback concerts, is criminally responsible for the singer's death because of medical negligence and his reckless use of propofol to help Jackson sleep.
The coroner ruled that Jackson's June 25, 2009, death was the result of "acute propofol intoxication" in combination with sedatives.
Dr. Cooper had recommended at 12:57 p.m., when Jackson was still at his home, that paramedics stop resuscitation efforts and declare him dead. Jackson was the first patient she had ever treated in the emergency room after having made such a recommendation to paramedics in the field, she said.
"I have never given a time of death in the field and then have that patient brought to me," she said.
She said this exception was not because Jackson was a celebrity, but because the patient had a physician with them who did not want them to give up.
Prosecutors have criticized Murray, who is a cardiologist, for using propofol on Jackson, contending it should be used only by anesthesiologists who have proper monitoring equipment.
Cooper, a prosecution witness, acknowledged under questioning by defense lawyer Michael Flanagan that she uses it regularly as an emergency room doctor.
A Houston, Texas, doctor called by the prosecution Monday paid Dr. Murray a compliment Monday afternoon, saying she was "impressed" with Murray's ability to remember a patient and that patient's treatment when she called him "out of the blue."
Dr. Joanne Bednarz-Prashad's testimony was important for the prosecution because she is one of the several people who spoke to Dr. Murray on the phone the morning Jackson died. Prosecutors say he effectively abandoned Jackson by leaving his bedroom to talk on the phone that morning.
Dr. Bednarz-Prashad called Murray's cell phone to get his advice on a patient he had treated who was about to undergo surgery at a Houston hospital. Most doctors she calls in such circumstances have to call back after consulting medical charts, she said, but Murray recalled the correct information immediately.
Prosecutors also called the first of three of Murray's girlfriends to the witness stand to talk about their conversations with the doctor just before he realized Jackson had stopped breathing
The judge prevented the prosecution from digging into the personal relationship between Murray and Bridgette Morgan, who previously testified at Murray's preliminary hearing about meeting the married doctor in a Las Vegas night club in 2003.
Morgan's call to Murray came about 30 minutes before Murray apparently discovered there was a problem with his patient.
Sade Anding, a cocktail waitress who met Murray when she was working at a Houston steakhouse, is likely to be one of the first witnesses Tuesday. Anding testified in January that she was on the phone with Murray when he suddenly stopped responding to her just before noon the day Jackson died.
That is the moment prosecutors contend Murray first realized that Jackson had stopped breathing. "I didn't hear him on the phone any more," Anding said. "I heard commotion as if the phone was in a pocket and I heard coughing and I heard a mumbling of voices."
Anding said she stayed on the phone for another five minutes, listening and wondering why the man she sometimes dated wasn't responding. "Hello, hello, are you there?" she testified she said.
The timing of the phone call is key to the prosecution's time line of when Murray realized his famous patient was dying. Based on testimony so far, the moment came at 11:57 p.m.
Nicole Alvarez, the mother of Murray's youngest child, may follow them on the witness stand. Her testimony is especially important because the propofol Murray used on Jackson was shipped to her Santa Monica, California, apartment.
Alvarez, 29, who met Murray around 2005 in a Las Vegas gentlemen's club, made it clear when she previously testified that she knew little about the doctor's activities.
"Dr. Murray and I were on a need-to-know basis, and I just know my place and my position in his life," Alvarez said.
Murray called Alvarez from the ambulance as he accompanied Jackson to the hospital, according to testimony in the preliminary hearing.
Representatives from two cell phone companies testified Monday morning about records of calls to and from Murray's cell phones the morning Jackson died. The call times play a key role in determining the time line of what Murray was doing in the hours before Jackson's death.
The judge instructed lawyers not to disclose their witness list ahead of time. However, the prosecution has been following the same order of witnesses used in Murray's preliminary hearing in January.
Los Angeles Police homicide Detective Dan Myers, who led the Los Angeles Police Department investigation of Jackson's death, is likely to testify Tuesday or Wednesday.
Los Angeles County Coroner Investigator Elissa Fleak will probably testify within the next two days about searching Jackson's home after his death. She said at the preliminary hearing that she found seven pill bottles on the nightstand next to Jackson's bed and an empty bottle of propofol on the floor near his bed.
Murray's defense lawyers contend Jackson caused his own death by swallowing eight lorazepam pills and orally ingesting propofol while Murray was out of the room.
The judge imposed a gag order Friday, preventing lawyers for Murray from talking to reporters about the case. His order came after he learned Matt Alford, a law partner to lead defense lawyer Ed Chernoff, gave a television interview to NBC's Ann Curry on Friday morning.
If convicted of involuntary manslaughter, Murray could spend four years in a California prison and lose his medical license.