Former Inspector General Gerald Walpin's determination to investigate further the alleged misuse of AmeriCorps funds may have led President Obama to fire him, a Republican member of the board overseeing the volunteer agency alleged to a Washington newspaper.

If true, the assertion contradicts an explanation provided by White House, which said Walpin, 77, was "confused" and "disoriented" at a recent meeting of the board, exhibited a "lack of candor" and "engaged in other troubling and inappropriate conduct."

Meanwhile, a bipartisan group of officials -- including four former U.S. attorneys, three former federal judges, one former attorney general and a former counsel to President Clinton -- sent a letter to the Senate Wednesday defending the integrity and competence of Walpin.

Walpin's dismissal came after he announced to the AmeriCorps board that he wasn't done with the investigation into the alleged misuse of federal grants by Sacramento Mayor Kevin Johnson, a former NBA star and an Obama supporter who heads a nonprofit education group, according to The Washington Examiner.

A probe by Walpin's office found that Johnson and his academy, St. HOPE, which received $850,000 in AmeriCorps money, had misused the funds and AmeriCorps volunteers for personal purposes, by having them help in political campaigns and even wash his car.

The U.S. attorney's office reached a settlement, under which Johnson and the academy reportedly were ordered to repay about half of the federal grants.

But a Republican on the board of directors of the Corporation for National and Community Service, which oversees AmeriCorps, told the Examiner that Walpin wanted to issue a public statement asserting the need for further investigation into the case.

"Right now, when there is such a great emphasis on service, we did not need any press out there on this St. HOPE matter, which was already settled," the board member told the newspaper. "We thought he was going to use the press. He had an issue with the fact that a settlement was reached ¦and he was doing everything he could to continue to keep the issue at the forefront."

In an interview with FOXNews.com earlier this month, Walpin, who called the White House explanation "insufficient" and "baseless," said his performance at the May meeting drew criticism because he issued two reports critical of the board. In one, he criticized the settlement reached in the Johnson case; in the other, he criticized the use of millions of dollars for a program at the City University of New York.

"The board at that meeting was clearly angry at my temerity," he said.

First lady Michelle Obama's role in Walpin's dismissal has come under GOP scrutiny after press reports indicated she was taking a strong interest in AmeriCorps activities and when her former chief of staff, Jackie Norris, became a "senior adviser" to the CNCS.

In the bipartisan letter sent to the Senate, the former officials state that they have known Walpin for many years.

"We have never seen Mr. Walpin to be "confused, disoriented [or] unable to answer the questions," they wrote, adding that such an allegation "is totally inconsistent with our personal knowledge of Mr. Walpin who has always, through the present day, exhibited a quick mind and a command of the facts (whether we agree with him or not) and eloquence."

Click here to read the Washington Examiner report.