Not familiar with Calgary, so I don’t know if it was a mall-attached-to-office-tower kind of mall that closes on the weekend.
If he climbed over the pony wall, slipped, and cracked his head on the plumbing pipes he may have been comatose or skull fracture that could be fatal.
I was thinking he suffocated for some reason. Poor airflow behind wall, build up of co2 replaces oxygen, he passes out and never wakes up.
For a drugged out street person, perhaps is was a good place to sleep (warm, fresh water, safe), only this time the person OD’d.
Posts like that that one of yours are why I like the SDMB. 
That’s pretty much what it is–a downtown mall connecting a series of office buildings across a few blocks. Elevated and enclosed walkways cross streets where necessary, to keep the mall together.
I’ve been to that mall before. Like many downtown malls, it exists on a few levels; and the food court, where the washrooms are (and where the body was found), is on the topmost level.