Liberal law professor Alan Dershowitz on Saturday criticized Deputy Attorney General Rod Rosenstein’s continued supervision of the Robert Mueller investigation, citing “conflict of interest” as a reason he should be replaced.

“There is no surprise that this one is taking a long time,” Dershowitz said on “Fox & Friends” on the length of the investigation so far. “What is surprising is that Rod Rosenstein is still supervising it. More and more information is coming out about his conflict of interest. We have now seen stories in the New York Times about how he may have regretted writing a letter and he felt he was used writing a letter.”

“He is a central witness in this entire obstruction of justice if it involves the firing of Comey,” said Dershowitz. “How can he still stay on the case? I wish they would focus much more on that because he is recused. He is disqualified. He ought to be replaced. That will, however, slow the process down even more probably.”

Responding to a question from Ed Henry about ways to deal with the situation, Dershowitz cited several, including a lawsuit or an “ethics charge.” (RELATED: Congressman: Rosenstein Is Spying On Me)

“As somebody who has taught legal ethics for over 25 years at law school, the first thing you learn you can’t be both a prosecutor and a witness,” he said. “So much influences your role as a prosecutor to know that if the case goes a certain way, then you are a witness. If it goes another way maybe you are not a witness. You will look terrible this way. You will look better the other way. He has real self-interest. People talk about the president not pardoning himself or the president not pardoning people who are involved. Here you have the person who is leading the investigation who has an obvious interest in the way in which the investigation is going to go involving his own participation. That just shouldn’t be allowed.”

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