Los Angeles ( CNN ) -- Michael Jackson 's estate never gave an expert it hired permission to help AEG Live defend against the wrongful death lawsuit filed by Jackson 's mother and children , the estate 's top lawyer said Thursday . The revelation raised questioned about the testimony of entertainment industry consultant Eric Briggs , who was hired by AEG Live to challenge the Jacksons ' expert opinions concerning damages the concert promoter might owe if found liable in the singer 's death . Briggs told the court this week that his company -- FTI Consultants -- had gotten a waiver from a Jackson estate lawyer before agreeing to work on the concert promoter 's defense . Briggs had signed a confidentiality agreement with the Jackson estate in 2010 when he was hired to determine the value of its biggest asset -- the Sony-ATV music catalog that includes the Beatles songs -- for the estate 's tax filings in 2010 . He was hired by AEG Live lawyers in February to prepare a challenge of the opinion of an expert hired by the Jackson lawyers to calculate how much money the singer would have earned had he not died while working on his comeback concerts in 2009 . Briggs said he -- or someone else in his company -- gained permission from the Jackson estate lawyer Jeryll Cohen to waive any potential conflict of interest . `` No one from the estate or any lawyers authorized or waived any potential conflict for FTI or Mr. Briggs , '' Jackson estate attorney Howard Weitzman wrote in an e-mail read in court Thursday . Such a waiver would be counter to the interests of the estate 's beneficiaries -- Jackson 's mother and three children , a Jackson lawyer said . Despite the conflict , the judge ordered Briggs to answer questions posed by Katherine Jackson 's lawyers about the music catalog . He said although his valuation placed Jackson 's interest in the catalog at about the same level as Jackson 's debt at the time of his death -- which he said was $ 400 million -- the IRS challenged it as low . An independent analyst hired by the IRS concluded he had undervalued Jackson 's interest in the catalog by up to $ 300 million , Briggs testified . Jackson lawyers argue it is evidence the singer was not broke when he died , contrary to what Briggs said in his testimony . Briggs testified this week that it was his opinion that it was speculative that Jackson would have earned a dime more in his life if he had not died of a propofol overdose on June 25 , 2009 . He based his opinion the testimony of a doctor who said earlier that he did not think Jackson would have lived even another week past that date . Panish , however , pointed out that the doctor 's opinion was based on the assumption that Dr. Conrad Murray would still be giving Jackson nightly infusions of propofol -- the surgical anesthetic the coroner said killed him -- as a treatment for insomnia . The Jackson 's suit contends AEG Live is liable because it negligently hired , retained or supervised Murray .
AEG Live 's consultant testifies Michael Jackson 's estate waived its conflict of interest . A Jackson estate lawyer contradicts testimony of consultant Eric Briggs . The IRS is challenging Briggs ' valuation of Jackson 's share of huge music catalog . Briggs calls assertions of Jackson 's potential earnings `` speculative ''