Episode #4.7 - S4-E7
Stupidity: It is stated that the police got the fingerprints of the culprit thanks to a certain object. In other words, they investigated the murder without taking any fingerprints from any suspect - even the one who has been jailed for shooting the corpse - and they even had his file already from the previous inquiries.
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
raywest ★