Paying others to take his tests for him.

You can change what's on a piece of paper. You can erase the "paper trail" if you get rid of the paper (and the right people). You CAN'T get rid of the computer evidence without committing another detectable and prosecuteable crime.  
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http://www.msnbc.com/transcripts/transcript-beat-ari-melber-5-27-21-n1268901
... "We`re joined now by Jack O`Donnell. He was president of Trump`s Plaza Hotel and Casino in Atlantic City. He`s the author of "Trumped! The Inside Story of the Real Donald Trump.""
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O`DONNELL: Well, it`s all about money with Donald. Everything centers around money with Donald and the organization. *****And there`s two forms of money. There`s cash, and then there`s what`s on a piece of paper, OK?***** And they don`t necessarily have to look the same, or they don`t have to total up the same. The numbers can mean something different. That was very clear.  And I actually went through a situation where I was asked to literally build false financials for my business. So, I know the numbers don`t have to equal each other.
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MELBER: Who requested that?
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O`DONNELL: Very specifically, three people were involved in asking me to redo the numbers, Robert Trump, his brother, Harvey Freeman, who was his attorney at the time, and ***Donald Trump*** also.
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O'DONNELL: And I was first put in a room with Robert and Harvey, and they said: "These numbers don`t -- won`t work. We can`t go backwards. The numbers have to go up."
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I said: "Well, we`re having a 20 percent increase in capacity. Everybody`s numbers are going to go down."
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They said: "Can`t have it. Allen won`t accept it. Donald won`t accept it. Have to redo the numbers."
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After that meeting, I then went into Donald`s office. And Donald said: "Did Robert and Harvey talk to you about the numbers?"
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And I said: "Yes, they did. But let me explain why I can`t redo the numbers, because they won`t be true."
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And he [Donald Trump] just said: "We need new numbers."
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When you wipe with a computer, it's too scratchy. Paper works best!

I was hoping for more comments on Reason #1, above.  O'Donnell, the President of Trump's Plaza Hotel and Casino, was called on the carpet and told to change the numbers on financial documents (that would have been subject to review by the NJ gambling commission).  
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O'Donnell said and is prepared to testify under oath that he told Trump in a face to face meeting, "I can`t redo the numbers, because they won`t be true." and that Trump then told him, "We need new numbers."