Legal help?

ok my dad works for a landscaping company and they had to fire someone. the company has a "tab" at lowes and after the person got fired he kept using the tab and buying stuff using my dad's signature.the police want lowes to file charges but they dont want to and the company cant file charges. could my dad file charges? and would it be forgery since he signed my dads signature? the police said it was not, they said it was grand larsony. what do we do? the person keeps getting his buddies to go and buy stuff and they catch them but they just say leave they do not arrest them.