Over the course of about three months in 1946, a masked killer stalked young couples on lovers' lanes attacking 8 people and killing 5.  No one was ever caught and convicted.  There are many theories on who the killer might have been, none were ever proven.

Sources: 

vault.fbi.gov/texarkana-phantom-moonlight-murders-part-01-of-02/view-02-of-02/view

morbidnmacabre.com/2020/08/28/the-texarkana-moonlight-murders/

www.texasmonthly.com/the-culture/texarkana-murder-mystery/

the-line-up.com/texarkana-murders

morbidology.com/the-texarkana-moonlight-murders/

www.nydailynews.com/news/crime/texas-murder-spree-hands-phantom-killer-solved-article-1.2554028#

www.texarkanagazette.com/news/texarkana/story/2016/mar/24/its-been-70-years-of-terror-stalked-texarkana-form-phantom/419177/

www.aymag.com/texarkana-famous-phantom-killer-part-1

www.aymag.com/texarkana-famous-phantom-killer-part-2

In 1989, college student Mark Kilroy and three friends took a trip to South Padre Island in Texas to celebrate Spring Break.  It was supposed to be a fun time to blow off steam and relax after a busy few months at school.  Unfortunately, the trip ended in tragedy with Mark's murder.  Police would uncover a terrible crime scene based on ritual human sacrifice, drug smuggling and the cult leader who was responsible for all of it. 

Sources: