Investigators recommended that Army Maj. Gen. Geoffrey Miller be reprimanded for failing to oversee the interrogation of a high-value detainee that was abusive, said the aide.
But Gen. Bantz J. Craddock, commander of U.S. Southern Command, instead referred the matter to the Army's inspector general, said the aide, who described the still unreleased report on the condition of anonymity.
Craddock concluded that Miller did not violate any U.S. laws or policies, the report said, according to the aide.
The investigation also found that interrogators violated the Geneva Convention and Army regulations three times at the base, the aide said.
The aide described the report on condition of anonymity because the Pentagon has not released it.
The investigation also found that interrogators' behavior did not reach the level of torture or inhumane treatment, although it described instances of abuse or inappropriate actions by interrogators, according to the aide's description.
The investigation was conducted by Air Force Lt. Gen. Randall M. Schmidt and Army Brig. Gen. John T. Furlow after FBI agents' allegations of abuse at Guantanamo surfaced last year.
FBI agents at Guantanamo alleged that interrogators lit cigarettes in prisoners' ears and shackled them into a fetal positions for hours, forcing them to soil themselves.
Craddock, Schmidt and Furlow were set to brief the Senate Armed Services Committee on their findings on Wednesday.