Courts may convict accused to as many offenses as are charged and proved

Dear PAO,

My neighbor's brother was accused of kidnapping a family of three. Their family was shocked when the judgment came — he was convicted of three crimes, one for each family member allegedly kidnapped, even though only one complaint was filed against him. I have read that a complaint can only charge one offense, except when the specific law allows a single punishment for different offenses. So, is it possible for a person to be convicted of more than one crime when only one complaint is filed against him?