messy version is that the images people circulate as 'Hello Kitty true crime' come from two messy sources that kept colliding online.
One source is the horrific 1999 Hong Kong case commonly called the 'Hello Kitty murder' — a real, gruesome crime where the victim was tortured and part of the aftermath involved the use of a Hello Kitty item. Tabloids, shock sites, and later blogs recycled photos and lurid descriptions from that case, and those pictures became the macabre seed for a lot of later content.
The other source is internet culture itself: Tumblr, Reddit, Twitter, and imageboards started remixing, photoshopping, and staging kawaii-meets-gore images as memes or commentary. People blended vintage Hello Kitty merchandise photos with crime-scene aesthetics, and sometimes used real crime photos out of context. So when you see 'Hello Kitty true crime' pictures, they can be real-world crime photos tied to the 1999 case, manipulated/tabloid images, or outright fan edits meant to shock. I try to stay mindful of how these circulate — they’re unsettling, and often disrespectful to real victims, which always sits heavy with me.