The only citizen that Maryland Gov. Martin O’Malley (D) named to a once-in-a-decade redistricting commission was at the time of his appointment under investigation for failing to pay nearly $4 million in taxes and has since pleaded guilty to tax evasion.

Richard Stewart, a Prince George’s County businessman and longtime Democratic donor, faces up to five years in prison and has agreed to pay more than $5.4 million in restitution, according to a release by the U.S. Department of Justice.

While running Montgomery Mechanical Services, an air conditioning and heating business, from 2003 to 2008 in Capitol Heights and Baltimore, Stewart “did not collect, truthfully account for and pay” millions in social security and federal income tax withholdings, according to Justice.

Stewart did not immediately return a call seeking comment. O’Malley attended a public hearing Thursday morning on a plan that Stewart and four other commission members recommended for redrawing state lawmakers’ districts.

Prior to the hearing, O’Malley spoke to reporters about the revelations, saying he was deeply troubled by the news. O’Malley said he had no prior knowledge of the investigation or settlement, and that Stewart had never disclosed them.

Stewart did not immediately return a call seeking comment. O’Malley is scheduled to preside over a public hearing Thursday morning on a plan that Stewart and four other commission members recommended for redrawing the legislative districts of General Assembly members.

Despite his guilty plea last week, Stewart was held up Tuesday as a key guarantor of minority voting rights by the office of the state attorney general.

In October, Stewart endorsed a controversial plan to realign the state’s congressional districts. The plan has drawn legal challenges claiming that it dilutes minorities’ voting strength for partisan gain.

Most notably, the map splits majority-minority Montgomery County into three mostly white districts, including moving many left-leaning Montgomery voters into the Western Maryland district of Republican Rep. Roscoe G. Bartlett.

Stewart’s and commission chairwoman Jeannie Hitchcock’s endorsement of the map was stressed Tuesday by Assistant State’s Attorney Dan Friedman as he sought to convince a three-judge panel that Maryland’s new map is not a partisan or racial gerrymander. Steward and Hitchcock are African American.

David Ferguson, executive director of the Maryland Republican Party, said that revelations about Stewart’s tax evasion plea, calls into question “the integrity of the entire map.” Republican party officials began publicizing Stewart’s little-known guilty plea late Wednesday.

In a statement early Thursday, Ferguson called on O’Malley to remove Stewart from the commission.

“Governor O’Malley stood firmly with Mr. Stewart for over six months during this very difficult time in his life,” the statement said. “While the Governor’s loyalty to his political ally and friend should be commended, his over-riding responsibility is to the nearly 6 million people in Maryland to produce a just map that accurately reflects our political and natural boundaries.”

O’Malley said the commission’s work was completed after it’s final report was submitted last week. Hitchcock, the commission chair, however, led Thursday’s public hearing, and the commission’s other four members participated. A fifth empty chair sat to the side of the dais.

O’Malley’s office did not immediately respond to a request for comment.

According to state and federal records, Stewart contributed nearly $16,000 to Democratic politicians from Maryland since the time he failed to pay federal taxes.

Rep. Elijah Cummings (D) and former Prince George’s congressman Albert Wynn were among Stewart’s biggest beneficiaries. O’Malley, state Sen. Ulysses S. Currie, current and former Prince George’s County executives Rushern L. Baker III and Jack B. Johnson also received contributions.

O’Malley first appointed Stewart to the Maryland Stadium Authority in 2007. He said Stewart would immediately step down from his position at the stadium authority.

Stewart is scheduled to be sentenced in April by one of the same judges weighing a lawsuit against the state’s congressional map.