I believe the non-injured roommates were female. They have been fully cooperative. Stranger things have happened. This is definitely a very odd case. No break-in, nothing was stolen, the door was left open all night. No defense wounds.

As for the noise or lack thereof: Maybe. If people had been out drinking all night (speculation). If the roommates had ear plugs and a sound machine going (speculation).

Autopsy will show where the puncture/lacerations are and can learn a lot from there, depending on where the lethal wounds were it can take a lot of strength and force to puncture through and do it four times in quick succession. A person would be winded and likely covered in blood.