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Alan Dershowitz said the closed-door investigation headed by Special Counsel Robert Mueller is the "worst possible way" to examine Russian interference in the presidential election.

Dershowitz, a Harvard Law professor emeritus and lifelong Democrat, said on "The Story" Thursday that politics is playing too much of a role on both sides when it comes to the allegations of collusion between the Trump campaign and Russians and accusations of bias within the FBI. 

He stressed to guest host Trish Regan that since Day 1, he wanted a nonpartisan body of "distinguished Americans" - similar to the 9/11 Commission - to conduct a transparent investigation.

"Right now [Mueller's] investigation is behind closed doors. We don't know what's happening. They decide what to leak and what not to leak. It's the worst possible way of getting information and trying to cure a problem that affects Democrats, Republicans and all Americans," said Dershowitz.

Regan asked Dershowitz about Mueller's credibility, noting the recent calls from some House Republicans for Mueller to be removed. 

"I think we have real problems of credibility. But those are all going to help Donald Trump because the pressure is on Mueller to show the world that he can be fair," said Dershowitz, acknowledging it's the "hardest job in the world" to investigate a sitting president and that Mueller has "made too many mistakes." 

He said the onus is on Mueller to find "hard evidence of real crime outside of presidential authority."

Watch his full analysis above. 

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