We have been told each bedroom door has a number coded lock and each bedroom door automatically locks when closed.
Told that by previous residents of this house.
I‘m assuming any fully closed door was “locked“ unless the lock was broken.
Hm, I guess I haven't seen that article...link?
This one says that you can't hear anything in the house on other floors but mentions the rooms had locks (not that they lock automatically) but based on images online, the locks may have been changed since that resident lived there in 2019:
A former tenant of the Moscow, Idaho, home where four college students were murdered on Nov. 13 says he couldn't hear activity from other floors when he lived on the first floor.
And this one says you can hear everything:
A University of Idaho graduate who previously lived in the off-campus house where four students were killed is speaking out to ABC News.
Suffice it to say, I haven't put much stock in old tenant comments because they have conflicted. But would be interested to see the confirmation that the doors lock automatically if you have it handy!
Edit to include this link: Father of Idaho murder victim fixed lock at home in week before the killings
where it says: However, a recent photo posted on social media that shows a second-floor bedroom appears to show a knob on a bedroom door that does not appear to be a coded lock, says Banfield.