Kyiv, Ukraine CNN  — 

Mykhailo Yatsentiuk left the basement to make tea for his granddaughter just as the bomb struck. When he came to his senses a half hour later the entire middle section of his apartment block had been destroyed; the basement where he had been sheltering with his family and neighbors was engulfed in flames.

The Ukrainian government says 54 people died at the apartment complex on 2 Pershotravneva street in Izium, eastern Ukraine, on March 9, almost half of the building’s residents. Entire families were killed in the attack, including the Yatsentiuks, Kravchenkos and Stolpakovas.

Their fates remained largely unknown until a few weeks ago when Ukrainian forces pursuing a counter-offensive reclaimed Izium after six months of Russian occupation, revealing a mass burial site on the outskirts of the city.

Most of the residents of 2 Pershotravneva were buried there among more than 400 graves, few with identifying marks other than numbers daubed on rough wooden crosses.

After speaking to a survivor, ex-residents and family members, and reviewing photos and video taken in the aftermath of the attack and following the town’s liberation, CNN can now tell the story of what happened at 2 Pershotravneva on that day.

Only rubble remains between the two towers at 2 Pershotravneva in Izium, pictured on September 30. Multiple families sheltering in the basement beneath the central part of the building were killed.

‘I started shouting… No one answered’

All that was left of the apartment block were two towers on either side with a smoking pile of rubble in the middle.

Months later, after the liberation of Izium, Dmytro Lubinets, the Ukrainian Parliament’s Human Rights Commissioner stood in front of the ruins and declared the deaths of those killed there “as a result of an airstrike by Russian troops” part of “a genocide of the Ukrainian nation.”

Local residents say that after the airstrike, Russian forces attacked the building with tanks, which were firing from across the river.

When the smoke cleared, walls, floors and ceilings were torn off, revealing the homes of the people who had lived there. Many of them were now dead, buried in their own basement where they had been sheltering.

Yatsentiuk lost seven members of his family that day – his wife Natalia, aunt Zinaida, daughter Olga (also known by the diminutive Olya) Kravchenko and her husband Vitaly Kravchenko, their son Dima who was 15, Oleksii who was 10 and their 3-year-old daughter Arishka, the grandchild Yatsentiuk had gone to make tea for.

“I started shouting Olya, Natasha, Vitaly… No one answered,” he said. “When I got upstairs [to the ground floor], I sat down and started crying, screaming. Oh God.”

An image taken by survivor Mykhailo Yatsentiuk on September 30 shows the wreckage of his former home at 2 Pershotravneva.

‘It was clear then that people died in families’

Izium, with a pre-war population of over 40,000 is a small town, the kind where primary school classmates stay friends for life and families live in the same building for generations. Anastasiia Vodorez and Elena (Lena) Stolpakova grew up together.

Vodorez describes the Stolpakovas as a “very happy, tight-knit” family. “Friends always gathered at their place, because we had a lot of fun there,” she told CNN from the Czech Republic, where she has lived for the past four years.

When Russia’s invasion of Ukraine began, friends urged Lena to leave Izium but her father Aleksander refused to leave their home at 2 Pershotravneva street. When friends learned that Lena’s house had collapsed d