The Air Force general who overturned a sexual-assault conviction for a star fighter pilot vigorously defended his decision in a lengthy letter, saying that accusations that he did not take sex crimes seriously were “complete and utter nonsense.”

Lt. Gen. Craig A. Franklin, commander of the Third Air Force in Europe, said in a six-page memo that he overruled the guilty verdict from an all-male jury because he had nagging doubts about the accuser’s credibility.

Franklin also said he had a hard time believing that the defendant, Lt. Col. James Wilkerson, could have committed “the egregious crime of sexually assaulting a sleeping woman” given that he was “a doting father and husband” who had been selected for promotion.

The letter, dated March 12 and obtained by The Washington Post on Wednesday, is Franklin’s first explanation for why he took the unusual step of granting clemency to Wilkerson, who had been sentenced to a year in the brig and discharge from the Air Force. He has since returned to active duty.

Lawmakers and advocacy groups have expressed anger at the decision. Critics called it a sign of how some commanders are reluctant to hold troops accountable for sex crimes, despite a soaring number of such cases in the armed forces.

Lt. Gen. Craig Franklin. (AP/AP)

In his letter, Franklin said he realized it would have been “exceedingly less volatile for the Air Force and for me professionally” to have accepted the jury verdict. But after what he described as a meticulous review of the case, he said it “would have been an act of cowardice on my part and a breach of my integrity” to uphold the conviction given what he considered a weak case against Wilkerson.

“The more evidence that I considered, the more concerned I became about the court martial findings in this case,” Franklin wrote. “Accordingly, I could not in good conscience let stand the finding of guilty.”

Franklin is not a judge and did not observe the November trial at Aviano Air Base in Italy. As the senior officer in Wilkerson’s chain of command, however, he held the authority under military law to toss out the conviction for any reason.

His explanation further infuriated some lawmakers, who said he had no business substituting his judgment for the jury’s and questioned why he gave weight to evidence that had been ruled inadmissible at trial.

“That offends anyone’s sense of justice and fair play,” said Sen. Claire McCaskill (D-Mo.), a member of the Senate Armed Services Committee. She said parts of the letter “just set my teeth on edge.”

In response to political fallout over the case, Defense Secretary Chuck Hagel has proposed changing military law so senior commanders could no longer overturn convictions. While commanders could still reduce or eliminate sentences, they would have to provide a written explanation.

Hagel’s proposal has already attracted support on Capitol Hill and Franklin’s letter appeared to add to the momentum.

Reps. Michael R. Turner (R-Ohio) and Niki Tsongas (D-Mass.), who lead the Military Sexual Assault Prevention Caucus, criticized the general in a statement for “perpetrating the “blame the victim” culture that inhibits effective prevention and prosecution of sexual assaults in the military.