Son desperate for answers in wake of Iowa apartment collapse: 'My dad's in there and there's nothing I can do'

It's been nearly 72 hours since a Davenport, Iowa, apartment building partially collapsed, possibly trapping two men inside, including resident Branden Colvin.

Colvin's son, Branden Colvin Jr., said he feels helpless as he waits for answers.

"I know my dad's in there and there's nothing I can do ... wishing I could just run in there," Colvin Jr. told ABC News on Wednesday.

Colvin Jr. said he's not an emotional person, but when he was alone, he said he broke down crying.

"I just want to talk to him, give him a hug, hear his voice, anything," he said.

The six-story building partially collapsed on Sunday afternoon for unknown reasons.

More than a dozen people evacuated the building at the time and eight people were rescued in the 24 hours that followed.

On Monday, officials said there was no credible information that anyone was missing and the city was moving forward with plans for staging a demolition beginning Tuesday.

Then, on Monday night, a ninth victim, Lisa Brooks, was found alive inside and pulled out of a fourth-story window.

On Tuesday, demolition plans were put on hold as officials announced that five people were unaccounted for, including two men, Branden Colvin and Ryan Hitchcock, who may be inside.

Colvin Jr. said Brooks' rescue "gave me hope."

"I'm just trying to stick it out and keep having hope," he said.

But Colvin Jr. is frustrated with city officials, saying he wants responders to "just go in there and look for these people."

Officials said Tuesday they were working to determine the best ways to search as the building's condition worsens.

In a Tuesday afternoon search, several animals were rescued, but no human activity was detected, city officials said.

"The stability of the building continues to degrade," the city of Davenport said in a statement Tuesday afternoon. "The recovery of any unaccounted for individuals remains the priority of the City as operational planning progresses."

The owner and property manager said in a statement, "Our thoughts and prayers are with our tenants and families during this difficult time. We would like to thank the brave men and women of Davenport fire, Davenport police department, and all other first responders for their tireless efforts to ensure everyone’s safety. We have been working closely with the American Red Cross and other agencies to assist the displaced tenants."

They're also working to refund deposits to tenants, a property manager told ABC News.