What are some of the greatest unsolved mysteries of all time

See this happy family. They died not long after this photo was taken in what I can consider as a great example of why humans can be the most messed up species on Earth even to our own kind. The Setagaya family consisted of four individuals which included 44 year old Mikio Miyazawa, his 41 year old wife Yasuko Miyazawa, and their beloved children, 8 year old Niina Miyazawa, and 6 year old Rei. Their life came to a brutal end on December 30, 2000 when an unknown killer now referred to as the Miyazawa killer entered their house through the open window of the second floor bathroom at the rear of the house which he managed to do by climbing up a tree. The killer then went into Rei's room and strangled him while he was sleeping and killed him through asphyxiation. Mikio then rushed up to the first floor stairs after hearing the disturbance in Rei's room and fought and injured the killer until he was stabbed in the head with a Saichimi bōchō knife killing Mikio instantly. The knife broke so the killer later fought Yasuko and Niina with his broken knife until he used a Santorum knife from the kitchen to brutally murder them. The killer remained inside their home for a couple hours and used their refrigerator, computer, and first aid kit supplies to treat his injuries and even took a nap on the sofa in the second floor of the living room. After he left the house he vanished and was never heard from again and it's been 20 years since the Setagaya family murders took place but the police have yet to identify who the guy was. The Killer may not even be in Japan but in some other part of the world but regardless this is one of the most mysterious unsolved murder mysteries of all time. The Setagaya family may be gone but they’re not forgotten

What are some of the greatest unsolved mysteries of all time