Your first sentence may be technically correct as for retirement, but in all likelihood the cops involved, if they in fact were since that’s never been proven of course and maybe never will be, were likely in their 20s at the time, so not dead. Just now in their 50s.
Your second sentence is the problem with this case and has been from day one.
The initial investigation was sabotaged from the beginning with inside information leaks to various teenagers and other issues. The initial detectives were all good cops who tried their best and then eventually got replaced years later, coincidentally right about the same time DNA started becoming a big thing in law enforcement crime solving.
Then they supposedly solved it by charging four burnout idiots with it who supposedly “confessed” including one with a gun pointed at his head at one point during the “confession.” He had actually said something during the interrogation they really really didn’t want to hear.
It is still being monitored, and not just on the net.