Professor John Mee:

No, he did not really. The nature of a joint tenancy is unusual, but the idea is that both own everything. When a person is callously murdered, his or her interest disappears and the other person continues to have everything. We say that is not fair and that we cannot have it. To solve the problem, we could say we would split it in half, the potential half share everybody had at the beginning. The killer would go from having something that was really worth half, a joint tenancy that entitled them to occupy everything, to be turned into a half share in the future.