!Protect Your Soul, No need to commit murder to rip it apart

"How do you spilit your soul?"

“Well,” said Slughorn uncomfortably, “you must understand that the soul is supposed to remain intact and whole. Splitting it is an act of violation, it is against nature.”

“But how do you do it?”

“By an act of evil — the supreme act of evil. By commiting murder. Killing rips the soul apart. The wizard intent upon creating a Horcrux would use the damage to his advantage: He would encase the torn portion ...”