Do detectives really feel a guy's arms, find one arm is slightly more muscular that the other then declare them innocent because the killer must have been left handed? It seems like slim basis for clearing an otherwise obvious suspect, but I've seen them do this in more than one movie, starting with In the Heat of the Night.
The thing that bothered me about In The Heat of the Night was that Virgil Tibbs was a Philadelphia police detective. Philadelphia cops are well known for racism and brutality, but Virgil Tibbs is played as an effete intellectual among the thuggish White southerners. It could have been the other way around----Virgil Tibbs as a violent Coffin Ed Johnson/Grave Digger Jones-like big city detective among the bewildered, Andy Griffith-like Southern Whites.
I also didn't know that police detectives performed their own autopsies.
In the novels, Virgil Tibbs had a black belt in karate and a brown belt in Aikido. Sidney Poitier karate chops a guy in the sequel, They Call Me MISTER Tibbs! He did it wrong with his thumb sticking up, so it may be just as well that they didn't put him in a karate fight with the rednecks.