When people hear body parts they immediately tend to think of organs like heart, kidneys, etc. These are strictly regulated in western medicine and hard to skirt. The provenance of an organ is checked at every step from pre-donation to post-op. But bones, skin, tendons, etc are also body parts that are used in medicine and regulated but somewhat easier to skirt because a single donation goes to a myriad of donees and unlike solid tissue, they aren’t necessarily used right away.