By Jim Donovan

By Jim Donovan

PHILADELPHIA (CBS) – As the investigation into what exactly caused the collapse at the salvation army thrift store continues to unfold, some say signs of trouble at the demolition site were apparent days earlier.

Signs of trouble indeed. In fact people had taken photos of the demolition site and even shot video because of their concerns. Little could they imagine, what would happen in the end.

A YouTube video shot on Sunday shows workers using an excavator to knock down sections of the building adjacent to the thrift store.

It was activity like this that raised some eyebrows from passersby and should have raised some red flags according to Drexel University’s Abi Aghayere.

“There were some red flags obviously,” said Aghayere.

He has authored several books on structural engineering and is a dean at Drexel University’s Goodwin College.

After reviewing the video, he used a cardboard model to show us how a wall can become unstable if it isn’t properly supported and is left freestanding.

“So a wall that used to have support top and bottom all of a sudden doesn’t have support at the top, and they are removing the support at this level,” said Aghayere.

Aghayere says he had walked down that stretch of Market Street just days ago.

“I was worried about the fact that there was no protection no scaffolding,” said Aghayere.

Which he says leaves people and adjoining property vulnerable from falling debris.

“Given the fact that pedestrians are walking all over the place I expected there would be inspection of this demolition while it was going on,” said Aghayere.

We now learn that according to L&I, that isn’t the case. They inspect demolition sites prior to the work, and afterwards, but not while it’s going on. Meanwhile, Aghayere says just as engineers are involved when a building goes up, they need to be involved when one is taken down to be sure it’s stable in the interim.

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