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Los Angeles (CNN) -- Elvis Presley's death became a controversy at the Michael Jackson wrongful death trial as a man who promoted both artists' last tours testified.

AEG Live Co-CEO Paul Gongaware testified Wednesday that Presley died of a drug overdose, but when his own lawyer questioned him Thursday he changed his testimony to say Elvis died of a heart ailment.

Presley collapsed in the bathroom of his Memphis, Tennessee, mansion -- Graceland -- on August 16, 1977, at the age of 42. While his death was ruled the result of an irregular heartbeat, the autopsy report was sealed amid accusations that abuse of prescription drugs caused the problem.

How Presley died is relevant because Jackson lawyers argue Gongaware's experience as Elvis's promoter should have made him more aware of drug abuse by artists, including Michael Jackson.

He was in charge of producing Jackson's "This Is It" concert when Jackson died on June 25, 2009, at the age of 50. The coroner ruled his death was caused by a fatal combination of sedatives and the surgical anesthetic propofol.

Dr. Conrad Murray told investigators he gave Jackson nightly infusions of propofol to treat his insomnia. He was convicted of involuntary manslaughter, sentenced to four years in prison.

Jackson's mother and children are suing AEG Live, contending the concert promoter is liable in his death because it negligently hired, retained or supervised Dr. Murray.

AEG Live lawyers argue their executives had no way of knowing -- or reason to suspect -- that Jackson was abusing drugs as he prepared for the "This Is It" concerts they were promoting and producing.

"I had no idea" Jackson was using propofol in the weeks before his death, Gongaware testified.

Although he worked advance promotion on Elvis Presley's last tours -- under the direction of Presley manager Colonel Tom Parker -- Gongaware testified he never met Presley.

"Did you understand he had a problem with drugs?" AEG lawyer Marvin Putnam asked.

"I understood that later," Gongaware said. "There was a period of time when we didn't work. I didn't understand at the time, but I learned that it was a drug problem and the Colonel said he couldn't work."

Jackson lawyer Brian Panish confronted Gongaware with two e-mails he sent two weeks after Jackson's death in response to condolence messages from friends. They both read: "I was working on the Elvis tour when he died so I kind of knew what to expect. Still quite a shock."

But under questioning from Putnam, Gongaware said he didn't mean that he expected Jackson to die like Elvis. He was referring to the trauma of people losing their jobs because a tour is canceled, he said.

'I don't recall'

AEG's lawyer tried to rehabilitate Gongaware's credibility with jurors, who sometimes laughed at his repetition of "I don't recall" several dozen times under questioning by Panish.

After the jury left the courtroom Wednesday, Los Angeles County Superior Court Judge Yvette Palazuelas commented on the number of "I don't recall" responses. "We've had a lot of that," she said. "How much more of that?"

"Why could you not recall e-mails?" Putnam asked him Thursday.

"I had not reviewed them and had not seen them in years," Gongaware answered.

Some of the e-mails were new to him because he was so busy putting Jackson's tour together that he never read them, he said. "Mostly, it was just a time factor if it was something that didn't have to do with me."

Outside of court, Panish suggested it was Putnam's job as Gongaware's lawyer to prepare him by having him review e-mails before questioning.

CNN exclusively obtained video of Gongaware's deposition recorded in December and played this week for jurors.

Gongaware struggled in the deposition when Panish asked him about the e-mail Jackson lawyers call their "smoking gun" -- because it contradicts AEG's argument that they never hired or supervised Dr. Murray.

They say Gongaware's e-mail, sent 11 days before Jackson's death, shows AEG Live executives used Murray's fear of losing his lucrative job as Jackson's personal physician to pressure him to have Jackson ready for rehearsals despite his fragile health.

It was Gongaware's reply to an e-mail from show director Kenny Ortega expressing concerns that Murray had kept Jackson from a rehearsal the day before. Ortega also raised his own concerns about Jackson's health.

"We want to remind (Murray) that it is AEG, not MJ, who is paying his salary. We want to remind him what is expected of him," Gongaware wrote. But in his video deposition he said he could not remember writing it.

After conceding that he wrote it, Gongaware then seemed unable to explain what he meant by the e-mail.

"He needs cheeseburgers"

AEG Live's production manager for Jackson's tour e-mailed Gongaware 10 days before Jackson's death that perhaps what the singer needed to turn around his deteriorating health was to be feed some junk food: "He needs some cheeseburgers with a bunch of Wisconsin cheesehead bowlers... and a couple of brats and beers. Jeez."

John "Bugzee" Houghdahl wrote a more serious assessment of Jackson's condition four days later: "I have watched him deteriorate in front of my eyes over the last 8 weeks. He was able to do multiple 360 spins back in April. He'd fall on his ass if he tried now."

Gongaware testified that he disagreed with Houghdahl's opinion, saying he had no "particular concern" about Jackson's health and ability to perform.

MJ looked 'Skeletal'

AEG Live President Randy Phillips sent Gongaware an e-mail after Jackson's death to make sure he did not use certain rehearsal video in the "This Is It" documentary because it made Jackson look too thin:

"Make sure we take out the shots of MJ in that red leather jacket at the soundstage where the mini-movies were being filmed. He looked way too thin and skeletal."

Gongaware testified that he did not know why Phillips would ask that. "We didn't keep anything out based on what Randy wanted."

Another e-mail suggested Gongaware was concerned that musicians, dancers and singers who worked on the show might tell interviewers after Jackson's death that he was unhealthy at rehearsals.

"The only thing we ask is that they keep it positive and stress that MJ was active, engaged, and not the emaciated person some want to paint him as being," he wrote in an e-mail approving their interviews.

Gongaware is expected to remain on the witness stand through Monday.