Of course in the past a lot of cases were "solved" by basically blaming the murder on a local vagrant who happened to be in the area of the crime. The fact that things like DNA evidence are making this untenable is actually a good thing even if it means fewer cases are closed.

Not much revenue in solving murders these days. Parking tickets is where it's at!

But the murder rate is also going down. Seems like the less capable criminals know they can't as easily get away with it.

Murder rates are also down substantially since the 1990s. The leading theories include reduced lead exposure and fewer neglected and unwanted children thanks to reproductive healthcare. In either case, the missing murderers would’ve been more impulsive, more careless, and easier to catch. Many of the murders that go unsolved today, likely would’ve gone unsolved in the past, too.

Plus, some of the cleared murders in the past were simply blamed on innocent black men by a racist system. Look at the Innocence Project for examples. We still have a problem with all that, but surely it’s not as bad as it was in the 1970s.

Another contributing factor is that so much forensics and police resources are wasted on victimless drug crimes. It’s an lot easier to bust a corner boy selling drugs than to track down a murderer.

The sad truth is that they just don't care about most of the murders.

Isn't that the CSI effect? People assume they will be caught so they don't bother trying. The ones that do try, now have more info on how to avoid detection.