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Time. Weather. Conditions. The extremely difficult task of identifying Miami condo victims.

USA TODAY logo USA TODAY 7/1/2021 Kevin McCoy and Trevor Hughes, USA TODAY
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Corrections/clarifications: This story originally provided an incorrect name of the 1,642nd victim identified in the 9/11 attack on the World Trade Center. He was Scott Michael Johnson.

Emergency crews at the site of a collapsed South Florida condo aren't just battling summer weather, smoldering fire and dangerous debris in their race to find 149 unaccounted-for victims. They're fighting time, heat, water and other factors that will make it harder to identify the dead.

The longer the search takes, the more likely it is that human remains will have decomposed significantly, making DNA identification more challenging, experts say.

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On Tuesday, searchers completed the sixth day of painstaking work since the collapse. Officials say they consider it a rescue mission, not a recovery. However, no one has been found alive since Thursday amid the piles of broken and pulverized concrete, twisted metal, and dangling debris.

Rescuers continue to search through the rubble of the Champlain Towers south condo collapse in Surfside, Fla. on Tuesday, June 29, 2021. © Andrew West, The News-Press via USA TODAY NETWORK Rescuers continue to search through the rubble of the Champlain Towers south condo collapse in Surfside, Fla. on Tuesday, June 29, 2021.

Considering the conditions at the site and the time that's elapsed, "this really does come down to DNA analysis," said Victor Weedn, Maryland's chief medical examiner and a DNA expert on the faculty of George Washington University's Department of Forensic Sciences.

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Forensic science experts say DNA identification will take weeks, if not longer. But it probably won't take as long as past mass casualty events. That's partly because of advances in technology spurred by the 9/11 terrorist attack that destroyed the World Trade Center – and prompted a victim identification effort that continues today.

"It's been a fruitful 20 years in terms of DNA technology advances," said Tracey Dawson Green, a professor and chair of Virginia Commonwealth University's Department of Forensic Science. "Now, just a few cells of DNA are enough to do an identification." 

The challenge of identifying victims at collapsed condo

It's difficult to identify victims in a mass-casualty event like the collapse of the Champlain Towers South Condominium in Surfside, Florida. 

Investigators first look for clothing that family members would recognize. They also check for IDs in victims' pockets or purses. 

However, most residents were asleep when the 12-story building collapsed early Thursday morning. They may not have been wearing easily identifiable clothing and may not have had their driver's licenses.

The bodies of many victims may have been crushed in the collapse, making easy identification impossible. The next option for investigators is to look for teeth and dental work, which can be compared with dental X-rays. They look for signs of medical implants, which might have identification numbers, and check fingerprints against official records.

However, the force of tons of rubble may have pulverized jawbones and teeth. Exposure to South Florida's heat, humidity and rainfall, plus a smoldering fire, water and other liquids in the rubble, may have obliterated fingerprints, Weedn said.

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Those conditions have made the work slow. 

"The time that it takes is just so painful, and that's why this matters," said Julie French, a former DNA scientist with the Michigan State Police. "This brings closure to the families that are grieving, as fast as possible."

How investigators will use DNA to identify Surfside victims

DNA identification involves comparing a DNA sample from bodies or body parts to other samples, such as those provided by close relatives or obtained from utensils used by the victims. Florida investigators began swabbing the cheeks of anxious relatives not long after the collapse.

However, it's not always possible to extract DNA. Body fragments may not have enough DNA to check for matches, and DNA degrades from exposure to heat, water and other elements.

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Moreover, DNA identification is complicated when fragments of multiple victims may be mixed together in the rubble.

"The longer it (the rescue and recovery effort) goes, the more difficult identification will be, simply because of decomposition," said Dr. Anthony Falsetti, a forensic anthropologist at George Mason University's College of Science. He worked on several major mass-casualty events, including the 9/11 World Trade Center collapse and the 1995 truck bombing of the Alfred P. Murrah federal building in Oklahoma City.

Some victims of the 9/11 World Trade Center attack have never been identified

After the 9/11 terror attack, the Office of Chief Medical Examiner of the City of New York led a massive effort to identify each of the 2,753 people killed in the collapse of the twin towers. Today, slightly more than 1,000 haven't been identified by DNA, in part because the fires from the collisions and jet fuel obliterated all traces.

However, that identification work never stopped.

In July 2018, nearly 17 years after 9/11, the medical examiner's office announced that advanced DNA testing had identified a 1,642nd victim, Scott Michael Johnson, 26, a financial worker.

Previous efforts to get sufficient DNA from a body fragment had failed. But new techniques used by New York City forensic investigators and similar labs have turned such failures into successes.

Mark Wilson, a 16-year veteran of DNA and other lab analysis for the FBI who's now an assistant professor at George Mason University's College of Science, explained the process.

First, part of a bone fragment, often from the femur, is pulverized to a fine powder, which makes extraction of DNA easier. Demineralization removes non-DNA material. After a few additional steps, investigators conduct amplification procedures on the DNA, readying it for comparison to samples from victims' relatives or investigative databases.

The advanced techniques have bought some time for investigators of the Surfside collapse and other mass casualties, said Dawson Green, the Virginia Commonwealth University forensic science department chair.

"The DNA community as a whole has gained a lot more experience," she said. "We can do things we weren't able to do before."

This article originally appeared on USA TODAY: Time. Weather. Conditions. The extremely difficult task of identifying Miami condo victims.

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