The trial began Thursday for the third soldier charged in connection with the death of Private Danny Chen.
Staff Sergeant Blaine Dugas is charged with dereliction of duty and making a false statement.
Defense attorneys in North Carolina argued Dugas was overseeing too many soldiers to monitor each one.
They said none of the soldiers reporting to him ever mentioned any abuse.
But prosecutors called several soldiers to the stand, who said the abuse was well known and Dugas must have known about it.
Chen, a Chinatown native, committed suicide while serving in Afghanistan last year.
Two soldiers have already stood trial. One pleaded guilty, while the other was convicted on minor charges.
Five other soldiers are also charged.
Meanwhile, the Army released a report showing a sharp rise in suicides among active duty soldiers.
According to the Department of Defense, there were 26 possible suicides among active duty soldiers in July.
One was confirmed, while the other 25 are under investigation.
That is double the number from the previous month and brings the year's total to 116 possible suicides.
Army officials say they are working to help soldiers deal with the stress of combat.
167 active duty soldiers took their own lives last year.