A prosecutor who quit the Justice Department over the Roger Stone case is expected to criticize the DOJ’s handling of Stone's sentencing during testimony on Capitol Hill on Wednesday, saying officials treated the political operative “differently from everyone else” because of his relationship with President Trump.

Assistant U.S. Attorney Aaron S.J. Zelinsky was subpoenaed last week to testify before the House Judiciary Committee as part of a broad investigation launched by Democrats into the “unprecedented politicization” of the Justice Department under the leadership of Attorney General William Barr.

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Zelinksy, in his prepared opening statement, is expected to testify that the sentencing for Stone was handled in an “unusual and unprecedented way.”

“What I saw was the Department of Justice Exerting significant pressure on the line prosecutors in the case to obscure the correct Sentencing Guidelines calculation to which Roger Stone was subject -- and to water down and in some cases outright distort the events that transpired in his trial and the criminal conduct that gave rise to his conviction,” Zelinsky is expected to say.

“Such pressure resulted in the virtually unprecedented decision to override the original sentencing recommendation in his case and to file a new sentencing memorandum that included statements and assertions at odds with the record and contrary to Department of Justice policy,” he continued.

He added: “What I heard -- repeatedly -- was that Roger Stone was being treated differently from any other defendant because of his relationship to the president.”

Zelinsky is also expected to say that the former acting U.S. Attorney for the District of Columbia Tim Shea was “receiving heavy pressure from the highest levels of the Department of Justice to cut Stone a break” and that his sentencing instructions “were based on political considerations.”

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“I was also told that the acting U.S. Attorney was giving Stone such unprecedentedly favorable treatment because he was ‘afraid of the president,’” he is expected to say, noting that it was “deeply unsettling.”

Stone, in February, was sentenced to three years in prison, after being convicted in November 2019 on seven counts of obstruction, witness tampering and making false statements to Congress on charges that stemmed from former Special Counsel Robert Mueller’s investigation.

Federal prosecutors had recommended a prison sentence of 87 to 108 months for the charges, but in a reversal, senior leadership at the Justice Department, including Attorney General William Barr, overruled and scaled back their recommended prison sentence. The sentence, as is customary, was ultimately determined by the federal judge in the case.

Stone has yet to report to prison because of the coronavirus pandemic.

Zelinsky is also expected to detail his decision to resign from the case, after he “immediately and repeatedly raised concerns, in writing and orally, that such political favoritism was wrong and contrary to legal ethics and Department policy.”

“Our objections were not heeded,” he will say.

“When I learned that the Department was going to issue a new sentencing memo, I made the difficult decision to resign from the case and my temporary appointment in the U.S. Attorney’s Office in D.C. rather than be associated with the Department of Justice’s actions at sentencing,” he will say. “I returned to the U.S. Attorney’s Office in Maryland, where I work today.”

Zelinsky will also say that his “concern” is not with the sentencing outcome for Stone, but “about process and the fact that the Department of Justice treated Roger Stone differently and more leniently in ways that are virtually, if not entirely, unprecedented.”

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U.S. District Court Judge Amy Berman Jackson, while taking a firm stance toward Stone in the courtroom, also said the up to nine years originally sought by federal prosecutors was excessive. Her sentence of 40 months in prison was considerably less than that -- yet far more than the probation sought by his defense and certainly tough enough to keep speculation alive about a possible pardon from Trump.

Meanwhile, Zelinsky will testify Wednesday alongside another Justice Department official, John W. Elias, who “can speak to improperly motivated activity by the Antitrust Division.”

Their testimony comes Chairman Jerrold Nadler, D-N.Y., has said he is planning to subpoena Barr and compel his testimony on July 2 over the recent firing of the U.S. attorney for the Southern District of New York, Geoffrey Berman.

Fox News' David Spunt contributed to this report.