Updated

The chief federal prosecutor in a Detroit terrorism case that fell apart because of prosecutorial misconduct resigned on Monday.

Assistant U.S. Attorney Richard Convertino (search), a 15-year veteran of the U.S. Justice Department, is under investigation by the department over his handling of the case. The department is also investigating his handling of two 1990s drug cases.

Convertino said in a statement that he had been looking for the right time to leave and that the opportunity to defend Jay Morningstar (search), a Michigan state trooper charged with murdering a homeless man, provided "the right reason."

"I know what it is like to be falsely accused of having motives I do not possess," he said.

The Justice Department in Washington declined comment on Convertino's departure, and Stephen Murphy III, the U.S. attorney in Detroit (search), also would not comment.

Convertino led the case against four North African immigrants prosecuted in the first major terrorism trial after the Sept. 11 terrorism attacks. The case against the four alleged members of a Detroit terror cell was hailed by the Bush administration as a major victory against terrorism.

But in 2004 the Justice Department had the judge throw out the men's convictions after it was learned that some documents that could have aided the defense during the trial were not turned over by the government as required.

Karim Koubriti, Ahmed Hannan and Abdel-Ilah Elmardoudi of Morocco and Farouk Ali-Haimoud of Algeria were accused of forming a terror cell. Koubriti and Elmardoudi were convicted of conspiracy to aid terrorists and document fraud, Hannan was convicted of document fraud and Ali-Haimoud was acquitted of all charges.

"The prosecution committed a pattern of mistakes and oversights that deprived the defendants of ... evidence ... and created a record filled with misleading inferences that such material did not exist," the Justice Department said in court documents.

U.S. District Judge Gerald Rosen complied with the request.

The government issued a new indictment in December, charging Hannan and Koubriti with conspiracy to commit mail fraud for allegedly filing a false auto accident insurance claim. Hannan pleaded guilty and was deported. Koubriti is awaiting trial on the fraud charge.

Convertino has a whistleblower lawsuit pending against former Attorney General John Ashcroft and other Justice Department officials, accusing them of "mismanaging the war on terror" and violating the federal Privacy Act by leaking information involving him.

Convertino lawyer Stephen M. Kohn said the Justice Department did not force his client to leave and said the departure was not part of a deal with the government.

"This will not affect his lawsuit, but by resigning from the DOJ, Mr. Convertino will be able to open a private law practice in order to aggressively defend clients, including other victims of government abuse," Kohn said.

The Justice Department would probably drop any disciplinary action against Convertino now that he has resigned, said Wayne State University law professor Peter Henning. But any violations of the law, such as obstruction of justice, are another matter.

Fellow Wayne State law professor David Moran said prosecutorial misconduct rarely results in disbarment. That is because disciplinary authorities are reluctant to punish public servants and are often themselves former prosecutors, he said.