My uncle was murdered in a small town. The police department ruined the investigation.?

The police did not secure the the scene of the murder. Also the chain of custody was not doented on the weapon. Although it is certain that the gun used was the murder weapon we could not prove it really was the weapon that was sent off for ballistic testing. When this all went to trial it made the defenses case. They claimed self defense and won. The defense attorney was really good compared to the prosecuter. The prosecuter seemed as if he had never argued a case in his life... I don't even know how this guy made it through law school. My question is.... What can we do? The prosecuter was representing the state and not our family. Also the man does not have any money... so it would be pointless to file a civil suit against him. I just want to know if we have any rights.