Speaking to reporters on Wednesday, Gen. Mark Milley estimated that as many as 10 to 20 percent of the Army's total cases are not reported.
"The percentage is too high," he admitted.
After former Airman Devin Kelley opened fire at a church in Texas earlier this month, killing 26 people, it was revealed that the Air Force had failed to submit his conviction on domestic violence-related charges to the FBI. Had the FBI obtained his record, Kelley would have been legally prohibited from purchasing a firearm.
"It's not just an Air Force problem," Milley said. "It's a problem across all the services where we have gaps in reporting criminal activity of people in service when they're convicted or they get a dishonorable discharge or those sorts of things, getting that over the appropriate law enforcement agency."
Milley said there are a "significant amount of omissions" that show the U.S. Army needs to "tighten up" its reporting of criminal activity.
Following the deadly shooting in Texas, Secretary of Defense James Mattis ordered all of the military branches to review their procedures.
"We all know that the situation inside the Air Force that could have been any one of the services," Milley said.
According to the general, about 150 soldiers every year receive a general court martial and are dishonorably discharged from the Army -- just one of the categories of cases that would be required to be reported to law enforcement.
"We need to make sure every one of those is transmitted over to the civilian law enforcement agencies, the FBI for example," he added.
Kelley was not dishonorably discharged, but received a bad conduct discharge. Milley did not have the statistics on that specific discharge category immediately available.