On the night of October 30, 1975, 15-year-old Martha Moxley was brutally killed in her own yard. The case went cold for a quarter of a century, until the prime suspect would be arrested. In the end, this suspect would be freed, never to be tried again.
Sources:
https://allthatsinteresting.com/martha-moxley
https://www.cbsnews.com/news/martha-moxley-murder-timeline/
https://www.cbsnews.com/news/who-killed-martha-moxley/
https://marthamoxley.com/
https://en.wikipedia.org/wiki/Murder_of_Martha_Moxley
https://www.nytimes.com/topic/person/martha-moxley
https://www.findagrave.com/memorial/10016/martha-elizabeth-moxley
https://www.nytimes.com/1975/11/05/archives/murdered-greenwich-girl-is-buried.html