The search for survivors of an Iowa apartment building continues, as crews work to stabilize the structure to make it safer for recovery efforts.

An urban search and rescue team from nearby Cedar Rapids is at the site, transitioning from rescue to recovery mode, authorities said at a Friday morning news conference.

A partial search of the building "was completed before sundown last night and that has allowed us to move to the next phase of our mission: shoring, securing the building for control and recovery," Urban Search and Rescue Team Chief Rick Halleran said.

Halleran noted exterior shoring of the building has been a slow process, explaining the building has continued to shift and it has taken time for utilities to be disconnected.

Nearly 50 people from the state's two search and rescue teams, based in Cedar Rapids and Sioux City, have been on site, according to Halleran.

"Task Force 1 has installed exterior shoring on the walls deemed unsafe by our engineers. We are continuing to work with onsite commanders to provide search and rescue recovery capabilities in accordance with their needs," Halleran said.

Just days before part of the apartment building came crashing down, inspectors noticed a brick façade had separated from the interior wall and appeared "ready to fall imminently," according to a letter from an engineer.

The engineer said the "brick façade is unlikely to be preserved in place, but it can be brought down in a safe, controlled manner," the May 24 letter said. The engineer also said the interior wall of the downtown Davenport building appeared to be losing stability and is "causing deformation."

A repair permit was issued the same day, according to Davenport city records. And a May 25 site visit confirmed repair work had started.

Just three days later, the same part of the wall that was under repair collapsed, according to a CNN review of photos of the property released by the city.

The disaster crushed apartments in the six-story building and turned residents' homes into heaps of rubble.

While no deaths have been confirmed, three residents who lived in the collapse zone are still unaccounted for. Davenport officials are now asking the public for any information about Branden Colvin, Ryan Hitchcock and Daniel Prien.

"It is believed that these three individuals have high probability of being home at the time of the partial building collapse at 324 Main Street in Davenport, Iowa on Sunday, May 28 ... and their apartments were located in the collapse zone," Davenport's city government posted on Facebook.

"If you have specific information that can confirm this or indicate otherwise, please call 563-326-6125."

City records and permit reveal more clues

This wasn't the first time the section of wall that ultimately crumbled needed repairs, according to the city's permit and inspection records.

The renovation underway "was a similar repair" to what was done to the building earlier in the year, Rich Oswald, Davenport's director of development and neighborhood services, said at a news conference Thursday.

The previous repairs were ordered by the city after it received a complaint February 2 about an unsafe wall at the building from an electric and natural gas company, according to a spreadsheet from the city tallying complaints, inspection and site visit details, and corrective actions taken at the building.

When building inspectors and a private-sector structural engineer arrived at the scene that day, they determined there was "visible dilapidation" on a portion of the western "exterior and interior walls," the document said.

The initial repair work, according to a construction permit and the spreadsheet, took several months. It was completed May 1.

Weeks later, another inspection revealed problems with the brick façade separating from an interior wall, as noted in the May 24 engineer's report. In addition to fixing the façade, the structural engineer recommended a steel column be added to support a beam believed to have been bearing down on the affected wall.

When city inspectors did another site visit on May 25, they noted brick work had started, according to inspection notes on a permit issued by the city for the work.

There's no explicit mention of any work on the wall in the permit notes, and it's not clear at this time whether any work had been done prior to the collapse.

Photos taken May 25 by city inspectors and released by the city appear to show a void formed between the façade and interior wall, and crumbled bricks are seen in the space.

One photo, taken by a city inspector on May 25, shows wood planks leaning up against the building's western wall.

A son wants to 'run in there right now'

Now, as families of those missing agonize and wait, city officials are grappling with how to proceed.

Branden Colvin Jr. has been sleeping on the pavement outside the partially collapsed building, where his father may be trapped in the rubble.

The 18-year-old should be getting ready for his high school graduation Saturday. But he refuses to leave the scene -- even as officials warn the rest of the building could come crashing down at any time.

"If they told me I could, I'll run in there right now," Colvin told CNN, fighting back tears. "I haven't slept. I have been out here three days, at night, all night, just waiting for anything."

The family of Ryan Hitchcock has already accepted the likelihood their loved one is gone and supports the city's plans to carefully take down the rest of the building to prevent further harm, relative Amy Anderson said.

"Ryan wouldn't want anyone else to put their lives at risk," Anderson said at a news conference Tuesday.

"I don't discount that he could be trapped under there miraculously," she said. "But we don't want to see any more families lose their lives or anybody else be injured in trying to remove that rubble and have anything fall."

Woman holds out hope for veteran father

The daughter of Daniel Prien, another of those unaccounted for, told CNN she will continue to fight for her father until he is found.

Prien, 60, is a formerly homeless veteran who was placed in the apartment building with the help of a local organization assisting the homeless population, daughter Nancy Prien-Frezza said.

She said her father has been homeless most of his life and was hard to reach because he was constantly on the go and was not good with technology.

After officials released Prien's name Thursday, Prien-Frezza said the organization reached out to her.

"They told me that my dad had hitchhiked from Wisconsin to Davenport and stopped by their offices in September to ask them for help finding a home," she said. "He was finally doing well for himself and had his own place."

She is now asking for help finding her father.

"I do not want them to demolish the building until the missing are found or confirmed to not be there," Prien-Frezza said. "He's a very sweet and loving person. He should not and will not be dismissed because of his situation so I'll fight to find him and get justice for him."

Investigators probe cause of the collapse

The cause of the collapse has not been determined, but the city plans to turn over documentation including videos, photos and logs to an investigative team, the mayor has said.

The property owner's insurance representatives and structural engineers visited the site Wednesday to complete an independent structural damage assessment, the city said.

The owner of the building, Andrew Wold, has been cited for failing to maintain the structure in a safe and structurally sound condition, according to a court document filed Tuesday. He faces a $300 fine plus court costs if he is found guilty or doesn't contest the citation, the document says.

Wold's court date is set for June 9.