It wasn't even solved because detectives were actively looking at it - they received an (incorrect) tip, and decided to just check out what else was in the case, and ended up sequencing some DNA left in the vehicle. I imagine there are hundreds of thousands of such cases out there like that.
https://www.cnn.com/2024/08/25/us/charlotte-nc-cold-case-sol...
i mention this becaues the golden state killer was a police officer _and_ serial killer, and took advantage of the delay to kill over a great span of time.
This has very little to do with diligence and more with technology advancing.
And, while clearing murders is nice, wait until the equivalent RealPage gets hold of that database and starts discriminating based on your DNA.
Sometimes, there's just not enough available information to go on.
How would you solve the case if you knew there was a lady dead on the street, and then a few miles away there is an abandoned stolen car with a half smoked joint. No fingerprints.
Where do you go from there in 1989?