This story keeps getting more weird.

A terrible thing to happen,but if the 2 girls were actually in the house at the time 1 how did they not see or hear anything and 2 more worrying why wasn't it rang in some 8 hours later?
How do 4 people get stabbed to death and leave no trace for the other 2 girls see?
I smell a rat something doesn't add up also the police keeping quiet