I’m sure a gun was involved to keep the victims compliant. The gun would have made too much noise, going off 4 times.
The animals used the knives to keep things quiet.
Actually I read that most of the victims had blunt force trauma. The knife was torture as the police think they were tortured all night (hence the bad guys ordering pizza to be delivered). Guess they were trying to get more cash out of them...Thank goodness the two daughters were away at school...poor kids..