The bag containing her head, was weighed down, but not the rest?
In general dismemberment of a victim is usually for 1 of 2 purposes,
1) To satisfy a psychological need (Psychosis/Psychopathy)
or
2) To delay identification, usually because the offender is known to associate with the victim.
In the first case, the offender usually doesn't care, if certain body parts, are discovered, sometimes, they are placed, in positions to ensure shock (EG, Serial Killer Danny Rolling, put one victims, head on a mantle to shock those who found her body)
In the second case, things like the victims, hands, (fingerprints), body parts with identifiable tattoos, and the victims, head (facial id/dental records), are hidden, to delay identification...Why?
Because its usually someone close to the victim.
