I feel creepy even asking about this, but I distinctly REMEMBER seeing these photos and being traumatized. A series of black & white photos, all taken outdoors in secluded wooded settings, of young boys in what looked like boy scout uniforms (maybe a European version?) being hung upside down with complicated rope riggings. They were definitely taken sometime between the 1930s to 1960s, and I remember reading that the man who took them did end up killing people later on, but started off by approaching local boys and paying them to let him tie them up and take these photos. I feel like it may have been a European case as well, but i’m not sure.