City records show demolition and construction work had been going on for months next to a 96-year-old Brooklyn building at 1321 Flatbush Ave. that collapsed Wednesday night, killing at least four people and injuring at least 17 others.

Investigators are now examining the debris left behind to determine what caused the collapse, which shocked residents and left city leaders with unanswered questions.

Google Maps imagery shows the commercial building that once stood at the adjacent construction site.