I'm still reading through this thread so there might be some repeats, but here are some of my picks.
Taxicab Phone Discovery: In 2014, a student got into a Fijian taxicab and found an unclaimed cellphone in the backseat. In an effort to find the phone’s owner, the student thumbed through the device’s photos. Instead, he found
a 10-minute video of four people clinging to ship wreckage in the middle of the ocean. The video shows the victims raising their arms for help only to be struck by multiple rounds of gunshots. Someone in the background of the video repeatedly yelled in Mandarin over a loudspeaker (people speaking Indonesian and Vietnamese are also heard). Police got involved immediately after the video was posted and contacted Interpol for help identifying both the victims and the assailants. However, because the video was such poor quality, no faces were identifiable. Because of the poor quality of the video, and because it happened in international waters, it's likely this case will never be solved.
To me, the creepiest part (aside from the actual on-screen murders) is that
at the end of the video the murderers all smile and laugh and pose for selfies. They just murdered four people in cold blood and they're laughing about it. It's chilling.
The Circleville Letters: In 1977, a school bus driver named Mary Gillispie started receiving anonymous, angry letters in the mail. Someone had found out about her affair with the school superintendent and wanted her to call it off. Later, her husband Ron received a letter of his own, and after a few weeks trying to ignore the threats, he told his children he was taking his gun to confront the letter writer and promptly drove his truck into a tree. He was killed instantly. Years later, the letters began arriving again, though Mary had remarried the superintendent and had nothing left to hide.
Su Taraskiewicz: Su Taraskiewicz was a trailblazer. In 1992, Su was not only the first woman to work as a ramp supervisor at Logan International Airport, she also filed reports of the rampant sexual harassment she encountered on the job. Su was a standup worker, who refused to become involved in a credit card theft ring amongst airport employees. Susan was last seen at 1:00 A.M. on September 13, 1992. She didn’t return from getting a midshift meal–and co-workers punched her timecard in and out anyway. Due to return for another shift the next evening, she didn’t show again. And once again, her co-workers punched her timecard. Her body was found inside the trunk of her car on September 14, having been beaten and stabbed to death. It is suspected that either one of her co-workers involved in the credit card ring or an ex-boyfriend was responsible for her killing, but the case went cold about a year after her death.
Abigail Williams and Liberty German: On February 13, 2017, Abigail Williams and Liberty German were dropped off by Liberty’s older sister at an abandoned railway near a hiking path in Delphi, Indiana. The two girls promised to meet with a family member near a bridge later on that day, but the duo never showed up. At first the police didn’t expect any foul play, but the girls’ bodies were found the next day about half a mile away from the bridge. The only lead investigators had were Snapchat uploads of the girls walking along the railroad, and an unidentified man approaching them. The last thing that remains from their encounter is a chilling audio clip of the man saying, “Down the hill.”
This case has been mentioned before in this thread but it's worth reiterating because it's so disturbing. I can't imagine how scared those poor girls must have been when that man approached them. The fact that it's been three years and no justice has been found is depressing.
I have more cases but I'll stop here for now.