Hi,
Very good question!!
It's still called a suicide by Police Reports, etc.
It's also called suicide by many web sites, reporting on Multiple Personalities, saying these persons usually have a high rate of "suicide", not "homicide", as this link points out:
http://www.merck.com/mrkshared/mmanu...er188/188d.jsp
Guess no one would ever know "who" killed "who".