WASHINGTON — A two-star Army general faulted for failing to properly investigate sexual assault and other accusations against a colonel on his staff will be retired at one-star rank, the Army announced Wednesday.

The decision by Army Secretary John M. McHugh comes more than a year after Maj. Gen. Michael T. Harrison was suspended from his duties as commander of U.S. Army forces in Japan.

His case has been cited as evidence of why sex-crime victims say they don’t trust the military to protect them, despite efforts by senior Pentagon officials, including Defense Secretary Chuck Hagel, to make commanders accountable.

In March the Pentagon turned back an effort in Congress to strip commanders of the authority to prosecute cases, especially those related to sexual assault, and hand the job to seasoned military lawyers.

An Army inspector general’s investigation report released in April said that in March 2013, when a Japanese woman accused the unidentified colonel on Harrison’s staff of sexually assaulting her, Harrison waited months to report it to criminal investigators. That was a violation of Army rules.

Despite Harrison’s suspension, the Army brought him to the Pentagon to make him director of program analysis and evaluation for an Army deputy chief of staff. The Washington Post reported in April that he received an administrative letter of reprimand in December 2013 for mishandling the sexual-assault case and other complaints in Japan, but remained on active duty.

Under federal law, commissioned officers retire at the highest rank in which they are determined to have served satisfactorily.

“The secretary determined that Maj. Gen. Harrison’s highest grade of satisfactory service was as a brigadier general,” the Army said in a brief statement announcing McHugh’s decision.

By retiring one rank lower, Harrison stands to lose a substantial amount of retirement pay.