One of the major questions is, who owns the building and what is that owner's record and potential liability?
The man the New York Times once called the "undisputed Prince of Porn," Richard Basciano, owned that property along with several other dilapidated buildings along that corridor.
The 2-block strip along Market Street was once the home to Philadelphia's last XXX theater and littered with adult entertainment shops and peep shows.
Records obtained by 6abc show in February Philadelphia Licenses and Inspections approved two permits for the building to be demolished.
Basciano told philly.com earlier this year it was part of his plan to clean up his past and build a gateway to Center City.
In statement on Thursday Basciano's company, STB Investments, said:
"Our heartfelt thoughts and prayers go out to the people affected by this tragic event. Please know that we are committed to working with the City of Philadelphia and other authorities to determine what happened yesterday."
Basicano, who is in his late 80's, owns several pieces of property on that blighted stretch of Market Street known for its prime location and sky-high real estate values.
"For weeks they have been standing on the edge knocking bricks off," roofer Patrick Glynn told Action News. "You could just see it was ready to go at any time."
Glynn watched for the last week as the contractors knocked down the building one brick at a time.
"I knew it was going to happen, I seen it," said Glynn. "I said it 10 times every day. I said, 'It is going to collapse. It is going to collapse.'"
And Wednesday morning, it did.
"We heard a boom, we saw a cloud of dust, and we took off running," said Brian Mullens, who was working in the area.
L & I Commissioner Carlton Williams said proper permits were pulled, and the construction company who was handling the project is licensed.
The question now is if short cuts were taken that caused the building to collapse.
"We will wait," said Williams at a Wednesday afternoon news conference. "OSHA is handling the investigation as well."
The Mayor says L & I will be conducting its own investigation along with the fire department into what exactly caused that building to collapse, and what if anything could and should have been done to prevent it.