The police very obviously didn't suspect foul play, my suspicious mind assumes that's because one or more witnesses told police things to convince them foul play was unlikely. .
I wonder if it was possible to access the stairwell from the lane running behind Dundonald? Getting there via Church St. would be longer/much more likely to be seen.
Whoever it was, IMO, knew about the stairwell beforehand. It just seems way too convenient to have that kind of private/hidden yet easily accessible place handy.
No, I don't believe so. That other side is boarded up (the part that fronts onto Dundonald). In many photos you can see the boards blocking the lane.
https://scontent.fdet1-1.fna.fbcdn....=f5644d677cbcfe6625b84e670764bb4a&oe=5A26CA74
You can also see how accessible this stairwell is.