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With his baseball cap and thick white beard, Allyn Kilsheimer could be mistaken for a retiree if it weren’t for the team of construction workers trailing him and the long metal pole he carried as he surveyed the ground floor outside of the Champlain Towers North building.

“Here, to here, to here, to here,” he told the workers, tracing a square along a support structure built out of the building’s facade to indicate where he wanted radar testing done that would show the arrangement of the steel reinforcement beneath the surface.

The gruff 80-year-old, a structural engineer and veteran of forensic investigations at catastrophes like the Pentagon post-9/11 and the collapse of a pedestrian bridge at Miami’s Florida International University in 2018, was hired by the town of Surfside, Florida, one day after a condominium collapse last month that’s left 79 people confirmed dead and 61 still unaccounted for.

The north tower, a sister of Champlain Towers South, with the same design architect and structural engineer, has become his laboratory.

On Friday, CNN accompanied him as he traversed several floors of the 12-story building, ordering tiles pulled up from the pool deck and concrete samples drilled from the wall of a fifth-floor apartment for a series of tests that he hopes will help to explain the disaster scene down the beach.

“It’s one of the 13,000 pieces of the puzzle,” Kilsheimer said.

Allyn Kilsheimer was hired by the city to investigate the cause of the Surfside condo collapse.
Rosa Flores/CNN
Allyn Kilsheimer was hired by the city to investigate the cause of the Surfside condo collapse.

As first responders worked around the clock to pull people from the rubble, Kilsheimer and a different set of investigators have been collecting evidence about the fallen structure and its design and maintenance in search of clues that could identify who, if anyone, should be held accountable for its collapse.

The overlapping probes – involving homicide detectives, local prosecutors and government engineers – could take years to complete; and, any desire by survivors of the collapse or victims’ families for a criminal resolution will run up against a legal standard that makes charges in a case like this difficult to bring.

The evidence at the investigators’ disposal is growing by the day.

Scientists from Washington, DC, have used drones to take 3-D maps of the crash site and have tested the composition of the soil beneath it.

Rescue teams from Pennsylvania search the rubble of the Champlain Towers South on July 8.
Pedro Portal/AP
Rescue teams from Pennsylvania search the rubble of the Champlain Towers South on July 8.

The National Institute of Standards and Technology, the lead federal agency investigating the cause of the collapse, has begun interviewing people involved in previous inspections of the building.

And local police are sorting through more than 13 million pounds of concrete pulled so far from the pile. Among that debris, NIST investigators have tagged more than 200 pieces as potentially significant, authorities said Friday.

After two weeks on the scene, Kilsheimer says he’s considering “all kinds of possibilities” to explain the collapse. A number of factors, from design flaws to material deterioration, could have weakened the tower before a “trigger” event sent it falling, he said.

His team has investigated trigger theories that he thinks are highly unlikely, such as recent explosive tests carried out at sea by the Navy a few hundred miles from the tower. A car crashing into a pillar in the basement garage of the building is a more plausible trigger, he said, though no evidence of one in the weeks preceding the collapse has emerged as of yet.

“There may be something that we’ll learn as we’re looking at the debris that will help us understand what a possible trigger might have been,” he said.

Asked by a reporter what he would be looking for, he said, “something that doesn’t feel good in my gut.”

“We’ve been around the block a lot of times so I know what things kind of ought to look like, and I know what happens when they look a little strange, and then you have to evaluate the ‘little strange.’”

Earlier this week, the county’s top prosecutor, Katherine Fernandez Rundle, indicated that her office would wait for the results of the scientific investigation into the cause of the collapse before considering a criminal investigation.

Meanwhile, she said in a statement, she launched a grand jury to explore possible reforms to prevent similar collapses from happening in the future. That effort will culminate in a report similar to one a grand jury produced in the wake of the devastating 1992 Hurricane Andrew that led to improvements in building code.

Depending on the evidence that surfaces in the reviews by Kilsheimer and NIST, bringing a criminal charge would be a challenge, legal experts said, because of the high legal bar prosecutors would face to prove the most likely charge of manslaughter.

A man places flowers in the memorial that includes pictures of some of the victims of the collapsed Champlain Towers South condo building on July 8.
Joe Raedle/Getty Images
A man places flowers in the memorial that includes pictures of some of the victims of the collapsed Champlain Towers South condo building on July 8.

Under that charge, prosecutors must show “culpable negligence: that someone’s conduct was “gross and flagrant” with “reckless disregard for human life.”

Documents and reports that have emerged since the building’s collapse have so far painted a picture of a deteriorating 40-year-old structure and a condominium board that struggled to marshal the multi-million-dollar sum in time for needed repairs.

Frank Morabito, an engineer brought on by the board in 2018 to inspect the building, wrote in a report that year that “failed waterproofing” below the pool deck was “causing major structural damage to the concrete structural slab below these areas” and warned that failure to replace it in the near future would cause “concrete deterioration to expand exponentially.”

Infighting among the board followed over raising funds for the repairs, which rose in cost from an estimated $9 million to $15 million by 2021 as the condition grew worse.

“A lot of this work could have been done or planned for in years gone by. But this is where we are now,” the board’s President, Jean Wodnicki, wrote in an April 2021 letter to residents.

None of the reporting so far appears to have reached the threshold to charge culpable negligence, said Dave Aronberg, the state attorney in nearby Palm Beach County.

“Culpable negligence requires some knowledge that the building’s collapse was imminent and someone did nothing about it,” Aronberg said. “A report that says there’s a lot of structural damage and then the board didn’t shut down the building right away or the building (official) didn’t shut down the building right away – that’s not criminal.”

Rundle’s office still has an open investigation following the death of six people in the 2018 FIU bridge collapse, according to a spokeswoman for the office. The National Transportation Safety Review Board concluded in 2019 that design flaws and insufficient oversight contributed to that collapse.

This aerial photo shows part of the oceanfront condo that collapsed early on June 24.
Amy Beth Bennett /South Florida Sun-Sentinel/AP
This aerial photo shows part of the oceanfront condo that collapsed early on June 24.

Under Florida law, culpable negligence manslaughter does not have a statute of limitations.

In the Surfside case, prosecutors will also likely be guided by the eventual report from the NIST, the federal agency.

In an interview with CNN last week, Miami-Dade County Mayor Daniella Levine Cava said that the NIST had interviewed “a lot of people,” including municipal officials involved in the building’s inspection.

“Anyone who has any information at all they’ve interviewed,” she said.

Among the group is the building official for the town of Surfside, Jim McGuinness, who pledged to fully cooperate with the agency in a phone call with investigators, according to a spokesman for the town manager’s office.

Investigators from NIST also have subpoena power, although they’ve never used it, said Jennifer Huergo, a spokeswoman for the agency.

Huergo said the investigative team for the agency is still being assembled. People familiar with the agency’s work cautioned that a full investigation could take years to complete.

The FBI is not currently investigating the Surfside collapse, according to a US official, but a federal criminal investigation could be initiated depending on the NIST’s conclusions.

In the meantime, the first finding of potential wrongdoing would likely come in civil court, where lawsuits against the condominium board have mounted since the collapse, and where the standard for negligence is lower.

At a hearing this week, a court-appointed receiver representing the Champlain Towers South condominium board said he is investigating contractors who worked on the building in recent years as well as the developer of a luxury high-rise next-door to Champlain Towers South as other “potential defendants” in the case who could be held liable for the collapse.

Their addition to the case could significantly increase the amount of insurance money available to residents of the tower.

Members of search and rescue teams gather for a moment of silence and prayer at the memorial to the victims in the collapsed Champlain Towers South condo building on July 7.
Jose A Iglesias/Pool/Getty Images
Members of search and rescue teams gather for a moment of silence and prayer at the memorial to the victims in the collapsed Champlain Towers South condo building on July 7.

A judge overseeing the cases, Michael Hanzman, has said he wants to finish the proceedings and get compensation into the hands of victims within a year.

“This case is going to be moving at a rapid pace,” Hanzman said. “These victims want to know what happened, they want to be compensated to the extent possible, and I’m committed – the court is committed – to getting this behind them, at least from a legal standpoint, as soon as practicable.”

Kilsheimer, too, said he is going as fast as he can. He sleeps just a few hours each night before heading to the office at 2 a.m. so he can work without interruptions.

“It wasn’t an act of god, I don’t believe,” he said. “We’ll figure it out. There might be people that don’t like what we figured out, but we’ll figure it out.”