what type of attorney do I need to represent a case of botched investigation done by police?

My son was a student at Tennessee State university in 2015. He was with 5 so called friends and was murdered by one of them at a park in the pavillion by the campus. The detective in charge did not measure the scene of where everyone was standing at the time of the shooting. No forensics was done, no fingerprints were taken from the bullet or casing that killed my son. Two of the witnesses gave the detective a drawing of the scene and the detective threw them away. He sealed the crime area off for less than 12 hours and the crime area became tainted because benches were moved. There were other negligent acts that led to a non-guilty verdict due to lack of evidence.,