CHICAGO (CBS) — Chicago Public Schools CEO Forrest Claypool is resigning after a report concluded that he lied to ethics investigators.

“I have accomplished all I can accomplish at CPS,” Claypool said at a news conference. “Even good men can make stupid mistakes. I look forward to the next chapter.”

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Claypool leaves Dec. 31. Dr. Janice Jackson will be the new interim head of the nation’s fourth-largest school system.

Janice Jackson (CBS)

CPS Inspector General Nicholas Schuler alleged that the system’s top attorney, Ronald Marmer, violated the CPS ethics code, and that his close friend, Claypool, tried to cover up the violation.

Marmer, a former lawyer at Jenner & Block LLP, supervised a $250,000 CPS contract with the international law firm. At the same time, he was still receiving severance pay from them.

According to Schuler, six attorneys — four at CPS and two from outside firms — told school officials Marmer was violating the ethics code by supervising Jenner & Block’s work.

Only after CPS went to a seventh lawyer did Claypool get an opinion supporting Marmer, which came from J. Timothy Eaton, a lawyer who has donated to Claypool’s political campaigns.

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Initially, Claypool contended there was no ethics violation because Jenner & Block eventually agreed to work for free, and Marmer’s severance didn’t depend on bringing business to the law firm.

In a November letter, Claypool wrote, “I strongly believe there was no ethics violation.”

Leaders of the Chicago Teachers Union had called for Claypool’s firing due to these ethical shortcomings.

Initially, Mayor Emanuel tried to defend Claypool and cautioned against making “snap judgments” about the longtime public servant. On Friday, he praised Claypool for helping to steady CPS’s finances.