First Contact Protocol Violated - Need Advice on Diplomatic Crisis

The plasma storm cleared just as Lieutenant Vyx detected three Zephyrian vessels surrounding us, their weapons charged and demanding we surrender our 'stolen' archaeological artifacts. Doc Aria insists the relics we recovered from the derelict station belong to a extinct civilization, but these aliens claim we've desecrated their ancestors' tomb. How do you handle first contact when it starts with accusations of grave robbing?