What wasn't taped never happened

So, we learn that the US Central Intelligence Agency destroyed at least two videotapes of illegally kidnapped foreign nationals evildoers being tortured questioned because they were afraid that the existence of the evidence would expose agents to legal jeopardy.

But everything that the US government has done to these illegally kidnapped foreign nationals evildoers has been entirely legal so what's the problem? If only there were some law that prevents the destruction of the evidence of a potential crime that could now be used against them.