but you have to assume this is a person who has just killed their wife and children. he is already calculating how he's going to dig himself out of this (as evidenced by his pre-arrest interviews).
when someone does something as heinous as this their first thoughts MUST BE to remove evidence that a crime was even committed (right??). the making of their childrens' bed may be first on that list.
Edit to add: I make these statements cuz I remember what it was like trying to hide something I did wrong (eating the chips, calling boys, etc) from my parents before they got home from work.