Florida bridge collapse: Victim's family demands explanation

Florida International University students returned to class Monday for the first time since the deadly bridge collapse. Crews are still working to clear the buckled concrete, flattened cars and debris after Thursday's accident. The bodies of six victims were recovered and identified over the weekend.

The search for victims is over, but the search for answers has just begun, reports CBS News correspondent Mark Strassmann. 

Joe Smitha's neice, Alexa Duran, died in Thursday's bridge collapse.

"We all were in shock, obviously, the whole family," Smitha said.

He's demanding an explanation into how this disaster could have happened.
 
"I want to see some people be responsible. I want to see some people come up and step up and say, 'Hey the buck stops with me,'" Smitha said.
 
No one has done that, but there may have been warning signs of structural issues. 
 
Just two days before Thursday's horrific collapse, one of the lead engineers for the project left a voice mail with Florida's department of transportation: "Some cracking that's been observed on the north end of the span… From a safety perspective, we don't see that there's any issue there, so we're not concerned about it."

However, that message wasn't heard until Friday, a day after the incident.
 
"At the core of this investigation is: how did this happen? How could this happen?" asked Matt Morgan, attorney who represents a client who was injured in the collapse. "I believe that once the cracks were identified, the first step which should have occurred was that the lanes of travel should have been closed immediately until there was the solution and those cracks were repaired."
 
Florida International University and its contractors say they will cooperate with the ongoing NTSB investigation. 
 
"We have a sense of urgency of getting to the bottom of this accident," FIU president Mark Rosenberg said. "Right now, our focus is on the victims' families and doing everything in our power to comfort and support them."

Florida Sen. Marco Rubio said the tightening of the bridge's inner cables could have contributed to the collapse. But he said more testing needs to be done by the NTSB.