Harvard law professor emeritus Alan Dershowitz said former special counsel Robert Mueller should not tell Congress anything that is not already in his final report.
Dershowitz made his comments in a column posted on the Fox News website Tuesday.
"When former Special Counsel Robert Mueller testifies July 17 before two Democratic-controlled House committees about his investigation of Russian interference in our 2016 presidential election and possible obstruction of justice by President [Donald] Trump, Mueller should refuse to say anything about the investigation of Trump and his campaign beyond what is already in his report," Dershowitz wrote.
"If Mueller goes beyond his 448-page report he will commit the same sin for which then-FBI Director James Comey was rightly condemned when Comey went further than a prosecutor should ever go in public after making a decision not to charge a crime."
Dershowitz referred to the "outrageous" 2016 news conference Comey held to deal with the FBI probe of Hillary Clinton's handling of emails.
"Instead of simply saying there was not enough evidence to prosecute the then-Democratic presidential nominee, Comey expressed his opinion that Clinton was 'extremely careless' about her handling of State Department emails on her private server."
He maintained "the same principle that should have kept Comey from talking about the Clinton emails" should limit what Mueller will say.
Dershowitz added that "Democrats and Republicans alike should oppose all efforts to undercut the long tradition of prosecutorial silence when a decision has been made not to prosecute."