The skies above the quaint neighborhoods of cities like Kharkiv or the coal mines of the Donbas were an unseen kaleidoscope of death as artillery fired from a distance ruled the day after the Russian retreat in early April from the Kyiv area. Moscow had decided to try to win by attrition.

What did that look like?

Soldiers cowered in trenches, pressing their faces into the cold earth, trying to shrink into the ground as shrapnel and debris cut through the air around them. Neighborhoods were transformed into wastelands. Apartments burned, and the sides of homes were sheared off like post-apocalyptic dollhouses.

The dead soldiers are called 200s, the wounded 300s. The terms are repackaged jargon from the Soviet era when dead soldiers being sent home in zinc-lined coffins from Afghanistan were called “Cargo 200.”

The frontline is the “zero line,” and going there means being sent to “zero” or, to some, “the meat grinder.”

Airstrikes and gun battles are rare compared with the immense amount of shells flying through the air, so soldiers call them “aviation bombs” and “rifle battles.” One soldier who spent less than a month on the front line in the country’s east never fired a shot. But his company of 106 men had four 200s (killed) and 23 300s (wounded), he said.

“People can’t fight artillery with machine guns,” he added matter-of-factly.

Those caught in the middle, the civilians, have fared the worst.

Their senses become finely attuned. Every sound, at all hours of the day, is analyzed. Is it an incoming shell?

They rely on split-second calculations about whether to stay or go. Run or walk. Sleep upstairs or head to the basement.

The routine is exhausting, but they quickly begin to understand the acoustic differences between a 120-millimeter mortar and a 152-millimeter howitzer shell. They use words like “horror,” “nightmare” and “unimaginable” to describe daily routines. The cold damp nights in their basements end at first light.

They emerge and survey the damage around them, glad they are still alive and hoping their neighbors are, too.

Even by conservative estimates, tens of thousands of civilians and soldiers have died. By the Ukrainians’ own count, as many as 3,000 of their troops had been killed as of April 16. Two days later, Russia launched its eastern offensive, and by the end of May, President Volodymyr Zelensky of Ukraine said that as many as 100 fighters were dying every day. More recently, his government put the number closer to 200 a day.

The death toll for the two nations’ militaries is shrouded in uncertainty. While the Ukrainian government is cautious in releasing information about its own casualties, Russia has a history of keeping such information secret. As of Friday, the Ukrainian military claimed that more than 33,000 Russian soldiers had been killed since the war began. Like so many numbers in this war, their claims are impossible to independently verify.

The last time a Western official offered a public assessment of Russian losses was in April, when the British said at least 15,000 Russians had been killed in action.

As far as civilians are concerned, Ukraine’s chief of police, Ihor Klymenko, said on Monday that prosecutors had opened criminal proceedings “for the deaths of more than 12,000 people who were found, in particular, in mass graves” just in the areas controlled by the Ukrainian government.

Roughly 75 percent of all the bodies recovered so far were men, he said. About 23 percent women. And 2 percent were children.

At least 1,500 civilians were killed in the Kyiv region alone, Mr. Klymenko said, many found lying on the streets after Russians were forced to retreat. “Snipers shot them from tanks, from armored personnel carriers, despite the white armbands that the Russian military forced people to wear,” he said.

It may take years before the true number of dead is known. But it is already clear that Russia’s invasion of Ukraine has led to Europe’s deadliest conflict since World War II.

Occupied by Russian troops for a little over one month, Bucha suffered waves of violence first as fighting raged in its streets and left the burned carcasses of Russian tanks blocking a whole avenue.

Later, as the frontline shifted further south, Bucha became a second line of defense. Russian troops parked their vehicles in the yards of houses and occupied homes. They ordered residents off the streets or into basements. They detained men of fighting age, and assaulted women.

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Most were local residents, men and women, young and old, families, and even children. Their bodies were often left where they had fallen, or were buried by families or neighbors in their backyards.

More than 1,300 people were killed in the wider Kyiv region during the Russian occupation — 86 percent of them in Bucha district, and 419 people in the suburb of Bucha itself, Andrii Nebytov, the head of the regional police, said this past week.

The dead included the mother of Tetiana Sichkar, 20, shot in the forehead as she walked with her family from fetching a thermos of hot water; and two sisters, a retired teacher and her disabled sibling, who lived together on a small side street.

They also included Dmitrii Shkirenkov, 38, a Moldovan builder, stranded by war at his construction site and executed on video by Russian soldiers; and Roman Havryliuk, 43, a welder, and his brother Serhiy Dukhli, 46, and a third man, shot in their yard when Russian troops took over their house.

“They were not able to defeat our army,” Mr. Havryliuk’s son, Nazar, 17, said, “so they killed ordinary people.”

Oleksandr Chubko contributed reporting.

Many relatives of Russian soldiers have gone weeks or even months not knowing whether their sons, husbands and brothers are dead or alive. The Russian military bureaucracy, soldiers’ advocates say, appears to have been unprepared for the scale of the casualties in Ukraine. The Defense Ministry, in its last casualty announcement on March 25, set the count at 1,351 deaths. Western officials say the true toll now could be more than 10 times that.

Some families of the sailors who died aboard the Moskva, the flagship of Russia’s Black Sea Fleet, which had a crew of more than 500, are still struggling to learn the truth two months later. Dmitri Shkrebets, the outspoken father of one conscript aboard, published an angry Telegram post on Monday directed at President Vladimir V. Putin.

“Why are you pretending that nothing happened?” Mr. Shkrebets asked. “We will all die, but not all will be martyrs, someone will have to answer for the blood!”

It was a rare public expression of anger and frustration with the government from a military family. But for much of Russian society, the deaths “are not making such a stunning impression,” Sergei Krivenko, who leads a rights group that provides legal aid to Russian soldiers, said in a telephone interview. In most cases, professional soldiers, rather than conscripts, are dying. They come disproportionately from poor regions, according to Russian journalists who have analyzed death notices.

“They are perceiving deaths as — it’s hard to say ‘normality’ but, in some sense, normality,” Mr. Krivenko said.

Over a period of 12 weeks, as Russian shells fell indiscriminately on apartment complexes, hospitals and town squares, Mariupol became a symbol of Russia’s willingness to bring devastation and death to Ukrainian cities and the civilians who inhabit them. The bombing of a theater where an estimated 1,000 people were sheltering is still viewed as one of the most brutal single attacks of the war. According to a reconstruction of the attack by The Associated Press, 600 people died.

On Thursday, the top United Nations human rights official said that Mariupol was probably the “deadliest place in Ukraine” in the first three months of Russia’s invasion.

And the dead are being found all the time.

“The body of six-year-old Liza remained in a car for 10 days,” a message posted on the “Mariupol Now” Telegram channel on Tuesday night read. “She was shot along with her family when she tried to get out of Mariupol. Her mother lost both legs and was unable to attend her daughter’s funeral.” A picture of Liza showed a blue-eyed child with wavy curls.

The channel contains thousands of other painful images — buildings destroyed, announcements of people killed, apartments ransacked by Russian forces when they took over the city.

The government estimates that 22,000 people died in Mariupol, a figure that cannot be confirmed because neither international organizations nor Ukrainian officials can access the area. But Mr. Boichenko and others believe it is far higher.

When Mariupol was surrounded, people improvised morgues in local post offices and pharmacies. They buried the dead wherever they could, in playgrounds and yards. Often the graves were not deep enough, or the burial was interrupted by shelling. There were bodies everywhere.

Mariupol’s City Council released photos on Wednesday of what officials said was a morgue improvised near the Metro supermarket.

The photos showed rows of bodies laid out in the open. “The bodies are just lying on the asphalt, absorbing the full heat of the sun,” the officials wrote.

Stacks of wooden coffins were shown leaning against the wall of a warehouse.

The omnipresent corpses are creating a public health crisis, Mr. Boichenko fears.

“Doctors say thousands of people might die in Mariupol because of infectious diseases,” he said.

Occupying Russian forces have halted the process of exhuming the bodies in Mariupol, Mr. Andryushchenko said.

“The occupiers made the process of reburial of Mariupol residents as complicated as possible, shifting all the problems to the citizens,” he said. “Now it is necessary to wait for the investigator with the prosecutor to carry out the exhumation, take the corpse to Donetsk for a medical examination and only then bury it in a specially designated place. And at each stage we will have to pay.”

His death was later mentioned by President Volodymyr Zelensky. In an address to the nation, he reflected: “This is it: A 6-year-old boy on Moskovska Street is also, as it turned out, a dangerous enemy for the Russian Federation.”

For the children of Ukraine, just like other victims, the difference between life and death often amounts to chance.

Shells have torn through their homes. The convoys of cars driven by parents eager to evacuate their families have been riddled with bullets. Train platforms where they awaited passage to safety have been targeted.

Death can also come suddenly from the sky, as it did one Saturday in April when a Russian cruise missile struck the home of Valerie Glodan, 27, and her three-month-old daughter, Kira, in Odesa, killing them both.

“This use of explosive weapons in populated areas and attacks on civilian infrastructure must stop,” Afshan Khan, UNICEF’s regional director for Europe and Central Asia, said during a press briefing this past week. “It is killing and maiming children and preventing them returning to any kind of normal life in the towns and cities that are their homes.”

Since the first days of the war in February, the bodies of the dead are seen regularly but usually anonymously, lying on sidewalks after shelling, lined up in body bags at collection points, as hands or feet sticking out of the dirt in mass graves.

The deaths of Ms. Perebyinis and her children were documented from the moment of their death and in subsequent interviews with family members. Breaking down in tears for the only time in the interview about his dead family, a few days after the artillery strike, Mr. Perebyinis said he had told his wife the night before she died that he was sorry he wasn’t with her.

“I told her, ‘Forgive me that I couldn’t defend you,’” he said. “She said, ‘Don’t worry, I will get out.’”

As for Ms. Addario’s photograph, she later said that it had felt almost disrespectful to stop and take it, but that it was important to record the moment. Reprinted on the front page of newspapers and news sites around the world, it became a watershed for the argument of accurately portraying the costs of war on innocent civilians.

Asked whether he supported showing the deaths of his family in this way, Mr. Perebyinis said he did. “The whole world should know what is happening here,” he said.