There are a number of factors at play here, one is certainly, as others have pointed out, that police are taking less initiative on the job due to low morale and their own form of quiet quitting.
However another major issue is that people are not talking to police like the used to. People do not trust police with information and more so they do not trust police to protect them. Volunteering information on a murderer is dangerous you have to trust the system can protect you.
And finally, murder clearance rates were focused on in the 90s and sometimes that led to closing cases early or other bad practices to increase superficial metrics.
However another major issue is that people are not talking to police like the used to. People do not trust police with information and more so they do not trust police to protect them. Volunteering information on a murderer is dangerous you have to trust the system can protect you.
And finally, murder clearance rates were focused on in the 90s and sometimes that led to closing cases early or other bad practices to increase superficial metrics.