After a group of terrorists detonated explosives at hotels and churches in Sri Lanka on Sunday, the death toll from the attacks rose rapidly.

Within a few days, officials settled at 359 dead, making the bombings one of the deadliest terrorist incidents since 9/11.

But on Thursday, health officials in Sri Lanka backtracked, saying the toll could be almost one-third lower than the earlier number. A more accurate death toll, they said, might be closer to 250.

There could be a gruesome reason for the dramatic change.

As first responders tend to victims in large-scale emergencies, forensic anthropologists and other specialists work alongside them to evaluate pieces of human remains. The anthropologists try to mitigate the risk of over-counting the dead, but mistakes can happen.

One of the first steps they take should be to systematically label any recovered remains, said Victor Weedn, a forensic pathologist and professor at George Washington University.

Recovering three right index fingers, for example, could indicate that three people were killed. But if left fingers are also recovered, they could belong to the same individuals as the right fingers. Similarly, two recovered legs and one human trunk could initially seem to indicate three bodies, Weedn said, and turn out to be only one. This kind of miscounting can easily inflate a death toll.

And depending on the type of attack, the fragmentation of human remains can make collection and counting even more complicated.

“You may have hundreds of pieces of one person,” Weedn said. That makes it difficult to identify them and difficult to know what to collect from the scene where they died. “How about something as big as your finger ... what about a grass blade with blood on it? It’s a slippery slope — you don’t know where to start and stop.”

Joe Hefner, a board-certified forensic anthropologist who teaches at Michigan State University and assisted in the aftermath of the 9/11 attacks, told The Washington Post that victim identification is always secondary to securing the scene of a crime. That would have been difficult in Sri Lanka this week, where there are ongoing security threats and officials continued to find explosives after the initial attacks were carried out.

When a death toll jumps and then comes back down, Hefner said, it typically isn’t the result of negligence. “I suspect that something like this would even overwhelm most local resources in the United States,” he said. “There are very few medical examiner systems that can handle an incident this big."

In cases where bodies are fragmented, forensic anthropologists use different approaches “to get as much information as quickly as possible,” Hefner said. Oftentimes, specialists can look at a fragment of bone as small as one to two centimeters long and be able to identify which bone it is and which side of the body it came from, using what Hefner described as a “mental template” developed over years of study and practice.

They also look for clues that can give even more information about the victim, such as how old the individual may have been, what sex they were, as well as their estimated height and their ancestry. “That’s what a forensic anthropologist can bring to the table, narrowing down who that [bone fragment] can potentially be,” Hefner said.

But in a chaotic situation such as the aftermath of a terrorist attack, there may be different investigators adding up their own numbers without realizing they are duplicating their colleagues’ work. Duplication is even more common in scenarios when bones may have been broken into many pieces, Hefner said. “The proximity and the explosive type is going to dictate what kind of fragmentation you see,” he said.

And this can all be complicated as the identification becomes personal, with thousands of people reporting their loved ones missing. In crises such as plane crashes, where a manifest of all passengers exists, it’s easy to know who was killed. When Hefner responded to the 9/11 plane crash in Pennsylvania, for example, he knew exactly what he was looking for: 44 people were on board United Airlines Flight 93, including the four men who hijacked it.

But in Sri Lanka, the attacks took place in open spaces, during church services and in hotels.

When a manifest doesn’t exist, officials will often try to create one by setting up call centers that allow loved ones to phone in details about their missing family members or friends. But that, too, requires well-trained workers who ask specific questions to avoid duplicating the numbers in their system as they track the missing.

And in Sri Lanka, authorities shut down Facebook and WhatsApp in the aftermath of the attacks, which may have made it even more difficult for people who survived to check in and confirm they were okay — or for concerned relatives to send in details about the missing.

Counting the dead is complicated in the aftermath of any large-scale emergency, and mistakes are likely to occur. In the case of Sri Lanka, “chaos is clearly part of it," Weedn said.

“I doubt negligence is part of it, but it might be that they’re not prepared for a disaster like this,” he said.

It’s hard to be.

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