Gen. John Campbell, the top commander of U.S. and allied troops in Afghanistan, told officials privately that he believes U.S. Special Operations Forces did not follow protocol when ordering an airstrike that destroyed a Doctors Without Borders hospital in Kunduz.

The attack, which lasted a half hour and killed 22 people, came after Afghan troops requested air support to take Kunduz back from the Taliban on Oct. 3. Campbell took responsibility for the error, but offered little explanation about the events that led to the strike or the procedures that caused the failure.

In his testimony to the Senate Armed Services Committee on Oct. 6, he said a fuller account would be made public, adding, “I must allow the investigation to take its course.”