WASHINGTON  An internal Justice Department investigation concluded Monday that political pressure drove the firings of several federal prosecutors in a 2006 purge, but said that the refusal of major players at the White House and the department to cooperate in the year-long inquiry produced significant “gaps” in its understanding of the events.

At the urging of the investigators, who said they did not have enough evidence to justify recommending criminal charges in the case, Attorney General Michael B. Mukasey appointed the Acting United States Attorney in Connecticut, Nora Dannehy, to continue the inquiry and determine whether anyone should be prosecuted.

The 356-page report, prepared by the department’s inspector general and its Office of Professional Responsibility, provides the fullest picture to date of an episode that opened the Bush administration up to charges of politicizing the justice system. The firings of nine federal prosecutors, and the Congressional hearings they generated, ultimately led to the resignation of Attorney General Alberto Gonzales last September.

The investigation, which uncovered White House e-mail messages not previously made public, offered a blistering critique of Mr. Gonzales’s management of the department. It called Mr. Gonzales “remarkably unengaged” in overseeing an unprecedented personnel review, and said that he “abdicated” his administrative responsibilities, leaving those duties to his chief of staff. It said that the process for deciding which prosecutors were fired was “fundamentally flawed.”