253. In any case not described in Section 250, 251, or 252 in which one person feloniously and intentionally kills another, any acquisition of property, interest, or benefit by the killer as a result of the killing of the decedent shall be treated in accordance with the principles of this part.
Section 251 is the joint tenancy section. It is NOT subject to Section 254 and the final judgment or conviction. Sec. 251 just says if one kills the other he can't take the property. Says nothing of a conviction being necessary, leading me to believe that all joint tenancy assets are effectively frozen until the matter is resolved.