Earlier quoted context omitted.
Selection bias is a cheap canned answer, but it doesn't make any sense here. Sensational unsolved crimes make the news. The public hearing about crimes isn't conditional on those crimes being solves. Arguably some of the most enduringly notorious crimes are the ones that go unsolved. The Zodiac Killer; never been caught. "D.B. Cooper", never caught. The presumed murder of Jimmy Hoffa, unsolved.
The best crimes do not look like crimes. The police does not put out press releases repeatedly with 'we got no leads'. Such cases fade fast.
Sure, but there is really no shortage of known unsolved crimes.
> The police does not put out press releases repeatedly with 'we got no leads'.
They do, in all the cases I listed they've asked the public for help for years. Certainly they don't do that for crimes they don't know occurred, but there is no shortage of known crimes that are very publicly unsolved.
For that matter, there are also a whole lot of missing person bulletins soliciting information from the public. Many of them might be murder victims, but it isn't known whether they are really alive or dead, let alone murdered. The public is nonetheless asked for information.