Maybe just the fact that the four victims were very close friends when compared to the other two people who were also in the same house and who were not killed.Lipstick message on the mirror, message in blood on the wall? Who knows? Could be anything. But if LE says there was something to lead them to believe the victims were targeted it has to be something out of the ordinary that stuck out to investigators. Something that ordinarily would not have been present in the crime scene.
No way to know until LE releases the information.
JMO