An emergency room doctor has told jurors that Michael Jackson's personal physician never mentioned that he had given the singer the powerful anaesthetic propofol.
But Dr Richelle Cooper acknowledged the disclosure probably would not have saved the King of Pop.
She recounted her conversations with Dr Conrad Murray on the day Jackson died, telling jurors in Los Angeles that he told her that he had only given the singer the sedative lorazepam.
She said under defence questioning that had Murray mentioned the anaesthetic, it probably would not have allowed doctors to save Jackson's life because he was "clinically dead" by the time he arrived at the hospital.
Dr Cooper resumed testifying as Murray's involuntary manslaughter trial began its second week.
Murray (58) has pleaded not guilty and his defence lawyers claim Jackson gave himself a fatal dose of sedatives and propofol, which is normally administered in hospital settings.
Authorities say Murray administered the fatal dose and acted recklessly by providing Jackson the drug as a sleep aid.
Dr Cooper testified she never asked Murray to sign a death certificate because, by the time he was brought to Ronald Reagan UCLA Medical Center, Jackson had become her patient.
" I didn't really have an explanation for why he was dead," she said.
Dr Cooper has previously testified she gave paramedics permission to pronounce Jackson dead, but that Murray wanted resuscitation efforts to continue. She has said more than an hour of resuscitation efforts at the hospital did nothing to improve his condition.
Dr Cooper also told jurors about trying to speak to Jackson's children after he was pronounced dead at the hospital at 2.26 pm on June 25, 2009.
"They were crying," she said. "They were fairly hysterical."
The physician's phone records are a central part of the case.
Prosecutors intend to show records of Murray's phone calls and emails from the hours before Jackson's death to show that the doctor had other things on his mind - getting his $150,000 (£97,000) a month deal to serve as Jackson's personal physician approved, running his practices and fielding calls from mistresses.
At a preliminary hearing, prosecutors showed Murray was engaged in three phone calls before he emerged from Jackson's bedroom and told a chef to seek help.