I can also recall someone claiming to own a human skull acquired through non nefarious means in real life.
What happens when the authorities find one in possession of a human penis or skull or an organ in formaldehyde or something? How easy is it to convince them it was acquired “legally”?
Very much depends on jurisdiction and what you’ve got. For example, the Native American Graves Protection and Repatriation Act (NAGPRA) criminalizes trafficking human remains that are identifiable as American Indian. On the other hand, my first college roommate, whose father was a dentist or oral surgeon, had a human skull that had been one of Daddy’s study specimens displayed on the shelf next to her desk, and there are places that will sell you one.
If you can show where you got it from, say a purchase receipt, that would be fairly definitive, but if you had some random body parts in your freezer, or human bones that looked or smelled ‘fresh’, that might raise an eyebrow or two. Unless they suspected that you were involved in some nefarious I don’t think the authorities would be too interested in what items you may have in your study… Native American remains notwithstanding.