Purity: Touching Separated Body Parts
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 516:
If part of the body of a living person, or part of the body of a dead person who has not been given ghusl, becomes separated and one touches it before it is given ghusl, it is not necessary for him to perform the ghusl for touching a corpse even if the separated part contains a bone. However, if a corpse is cut into pieces and one touches all or most of them, this ghusl becomes obligatory.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)