>> NARRATOR: Now, a special edition of FRONTLINE.

(phone dialing out) >> WOMAN (in Russian): >> SOLDIER (in Russian): >> WOMAN: >> SOLDIER: >> WOMAN: >> SOLDIER: (dramatic music playing, explosion) >> ERIKA KINETZ: At the start of the invasion of Ukraine, Russian forces expected to take the capital Kyiv within days.

(explosion) >> REPORTER: Explosions rocking several cities, including the capitol of Kyiv.

>> REPORTER: And there's little stopping Russia from threatening the capital Kyiv itself.

(rapid gunfire) >> KINETZ: But poor coordination and fierce Ukrainian resistance stalled the ground assault, causing a buildup of Russian troops in outlying towns like Bucha.

After a monthlong occupation, the Russians retreated.

>> REPORTER: Russia's withdrawal has revealed what looked more like crime scenes than the aftermath of battle.

>> KINETZ: They left behind evidence of war crimes that shocked the world.

>> REPORTER: Bodies bearing signs of torture and rape.

♪ ♪ ♪ ♪ >> KINETZ: I went to Bucha not long after the bodies were discovered, with my colleague, A.P.

videographer Sasha Stashevskyi.

Sasha.

>> Yeah?

>> KINETZ: He was based in Kyiv, and was one of the first journalists to arrive on the scene in early April after the Russian retreat.

We headed down a main thoroughfare called Yablunska Street, to a focal point of the killings, a nondescript office building that had become a de facto headquarters for the Russians during the occupation.

And what's the address of this building?

>> Yablunska 144.

♪ ♪ And here was... eight bodies.

Some of them was clearly shoot in the head.

tied hands.

And some of them had like eyes was... >> KINETZ: Blindfolded eyes.

>> Yeah.

Blindfolded eyes.

>> KINETZ: Yeah.

Sasha had documented what looked like the point blank execution of eight men and more bodies would keep turning up in Bucha.

♪ ♪ In the months since then, "Frontline," the A.P., and the visual investigations firm SITU Research obtained and reviewed hundreds of hours of CCTV footage, intercepts of Russian phone calls, and spoke with survivors and witnesses to show what happened in Bucha, and try to identify who was responsible.

♪ ♪ To better understand the scale of the atrocities, and how the violence unfolded, we built a comprehensive 3D model of Bucha.

It was based on data collected by a team of Ukrainian citizen researchers.

Bucha authorities say they recovered the bodies of more than 450 men, women, and children.

Nearly all of them showed signs of violent death.

We mapped where the bodies were found.

Each beacon represents the location of a victim, and each death, a potential war crime.

♪ ♪ The largest concentration of bodies-- nearly 40-- was recovered along Yablunska Street; which runs east to west in an industrial section of town.

We met with survivors along Yablunksa Street and beyond.

♪ ♪ (birds twittering) Natalia Vlasenko and her family lived just off Yablunska Street.

In early March, her 20-year-old grandson, Dima Chaplyhin, a store clerk, filmed the Russians arriving from this second floor terrace.

>> (in Ukrainian, crying): >> KINETZ: Dima wasn't the only one recording.

One private home on Yablunska Street was outfitted with six security cameras.

(gunshots) In the footage that we obtained, from March 3, Ukrainian soldiers try to hold off the Russian advance before retreating.

Soon after, dozens of Russian troops and vehicles marked with the letter V take over the street and continue to pour in.

By March 4, the occupation of Bucha was nearly complete.

That's when the Russians came for Dima.

>> (crying): >> KINETZ: Dima was rounded up as part of a Russian operation known as "zachistka" or cleansing.

Soldiers searched and interrogated everyone in the area to root out threats and terrorize locals into submission.

The CCTV footage offers a rare view of the Russian sweeps as they unfolded.

Some people were escorted with their belongings, even pets.

Others were taken by force, including this man who was gagged and pleading.

(man begging indistinctly) Russian soldiers brought people to their base at 144 Yablunska.

The building had been used as a bomb shelter before Russians took it over as their headquarters and base for interrogations.

They also set up a field hospital and held civilians who didn't pose a threat in the basement.

As the Russian sweeps continued, CCTV cameras also captured these nine men, including taxi driver Ivan Skyba, being led to 144 at gunpoint.

>> (in Ukrainian): >> KINETZ: When the Russians invaded, Ivan said that he and other volunteers had been manning one of three checkpoints set up along this stretch of Yablunska.

As troops advanced, volunteers from the other checkpoints escaped.

Ivan and his group hid in this nearby house before they were captured.

(computer mouse clicking) These are two different CCTV cameras, both of which are across the street from 144 Yablunska.

So we have two different angles on Ivan and the other guys being marched across the street.

(shouting on video) So the Russians are shouting at them, "To the (bleep) right, to the right, dumbass.

Where are you going?

To the (bleep) right."

And there they go off to the right, to 144 Yablunska.

>> SKYBA: ♪ ♪ ♪ ♪ ♪ ♪ (inhales deeply, sighs) ♪ ♪ ♪ ♪ >> KINETZ: Ivan said he waited for his moment.

Despite a head injury and gunshot to the abdomen, he managed to escape to this nearby house.

Within an hour, more Russian soldiers sweeping the area found him.

This time, they believed he was an injured civilian, and brought him back to 144, not to be tortured or killed, but to give him medical treatment.

>> SKYBA: >> KINETZ: On March 7, Ivan and the civilians sheltering in the basement were finally released.

The bodies of the men executed in the courtyard outside still lay on the ground, where they would remain for weeks.

That same day, after hearing that civilians were being let out, Natalia Vlasenko set out to 144 Yablunska to find her grandson Dima.

>> NATALIA (crying): >> KINETZ: But Dima was not among the civilians released.

Natalia would have to wait.

♪ ♪ The violence spread far beyond Yablunska Street.

When the occupation of Bucha turned from days to weeks, troops unable to reach Kyiv faced mounting losses, and they became more erratic and unpredictable.

(clattering) >> WOMAN (on phone, in Russian): >> SOLDIER (on phone, in Russian): >> KINETZ: In phone calls intercepted by the Ukrainian government, that we verified with the help of the Dossier Center in London, Russian soldiers admitted to killing civilians.

>> SOLDIER (on phone, in Russian): (phone dialing out) >> SOLDIER (on phone, in Russian): ♪ ♪ >> WOMAN (in Ukrainian): >> (in Ukrainian): >> KINETZ: They also took over people's homes.

Security cameras from inside this residence on Yablunska Street show soldiers playing with the lights, doing laundry, even chasing a dog.

They eventually discover the cameras and shoot them out.

Outside, on the streets and fields of Bucha, more bodies started to appear.

Those who were not able to flee hid inside their houses, including Natalia Vlasenko and her husband, Pavlo.

They stayed behind trying to find out what happened to their grandson Dima.

Near the end of March, Natalia said Russian troops returned to their house.

>> NATALIA: >> KINETZ: They began interrogating her husband, Pavlo, after discovering their son's military cap in a closet.

>> NATALIA (crying): (exhales, sniffles) ♪ ♪ >> KINETZ: By the end of the month, Russian forces gave up on their attack on Kyiv and pulled out of Bucha.

♪ ♪ Day by day, people found more bodies-- of their friends, families, and neighbors.

♪ ♪ >> (speaking Ukrainian, sobbing) >> KINETZ: Soon after Natalia buried her husband, Dima's body was discovered on the grounds of 144 Yablunska Street.

(sobbing) >> NATALIA: ♪ ♪ >> KINETZ: Dima was just one of the hundreds of bodies found throughout Bucha.

The full scale of the horrors, more than 450 deaths, wouldn't be known for months.

♪ ♪ What happened along Yablunska Street is now case number one for Ukraine's war crimes prosecutors.

Taras Semkiv from the Prosecutor General's Office is in charge of the case.

>> SEMKIV (in Ukrainian): >> KINETZ: Oh, God... These poor people.

>> SEMKIV: >> KINETZ: What do you think the odds are of you getting any of the people responsible for the atrocities at 144 Yablunska into an actual court of law and prosecuting them in a court?

>> SEMKIV: >> KINETZ: Semkiv said that those responsible for what happened to Ivan, Dima, and others on March 4 were from Russia's 76th Guards Airborne Assault Division.

>> SEMKIV: >> KINETZ: Those commanders are Major General Sergei Chubarykin, and his boss, Colonel General Alexander Chaiko.

♪ ♪ Ukrainian prosecutors are pursuing the generals for their roles in leading the invasion of Ukraine.

But they are still gathering evidence that could link them to specific crimes, like 144 Yablunska.

♪ ♪ The International Criminal Court in The Hague is also investigating potential war crimes cases.

♪ ♪ Bucha was a turning point, when the world called for accountability.

But with the war in Ukraine still raging, it is too early to say who will be held accountable for what happened in Bucha and beyond.

♪ ♪ Captioned by Media Access Group at WGBH access.wgbh.org.

>> For more on this and other Frontline programs visit our website at pbs.org/frontline.

♪ ♪ ♪ ♪ Frontline's "Crime Scene: Bucha" and "After Zero Tolerance" are available on Amazon Prime Video.