There have been urgent calls for investigations into allegations of war crimes in previously Russian-held areas of Ukraine after shocking footage of murdered civilians.
But there are wider questions over whether widespread Russian attacks on civilian targets amount to war crimes.
We've been looking at a series of attacks in one city - Chernihiv - to see whether they are consistent with Russian tactics across Ukraine and reveal something of their strategy.
The following report contains some graphic details.
1: Direct targeting of civilians
"They were shooting at us with everything they had," says Diana, 20. Within minutes of encountering the Russian tank, half her family would be dead.
Diana, her mother Irina, her partner Sasha and his little brother Maxim were fleeing Chernihiv on 9 March after weeks of shelling. They had one simple aim - to reach safety in the west of the country, where relatives were waiting for them.
But within minutes of leaving the city heading south they were plunged into danger.
As their Volkswagen Golf passed the village of Kolychivka, Sasha saw Russian tanks ahead. One fired at them immediately. He put his foot down, hoping to accelerate through the danger zone - and then the car stalled.
The firing continued, and Sasha shouted for them get out - but 15-year-old Maxim had already been hit. There was a hole in his chest and blood coming from his mouth.
Diana, Sasha and Irina crawled into bushes - but soldiers were approaching, shouting to each other, asking where the family were hiding. Bullets cracked towards them.
Diana's foot was seriously injured. Sasha tried to bandage it, but then as he turned to help Irina, the horror worsened.
"Irina opened her jacket and we realised that there was nothing to bandage," Diana told BBC News. "A part of her abdomen and intestines had been shot through."
They heard more shooting and Diana turned to Sasha believing these were their final minutes.
"We had time to say that we loved each other," she said. "I asked Sasha, 'Are we going to die here?' He said, 'Probably'.
"My mum crawled with us a little more. I kept turning and saying, 'Mum, crawl, please, please'. She said, 'Yes, yes'. And then she [lay] down on the ground. She died there."
Diana kept crawling, following Sasha as he broke a path for her through the thicket. They went past a burning field and through the forest.
Diana and Sasha survived and she made it to a hospital. She has lost four toes from her left foot.
Diana has no doubt the attackers were Russian because of their accents, uniforms and the Z symbol daubed on one of the tanks.
The BBC's verification team has found no evidence of any legitimate military targets near the site of the attack.
Attacks on civilians in cars elsewhere
- Regional authorities say at least 25 civilians, including six children, have been killed in attacks on cars trying to flee Chernihiv, or attacked in public places, since the start of the conflict
- Footage filmed by a Ukrainian drone in the Kyiv region showed the killing of a man who had raised his arms in the air as he got out of a car. His wife was shot dead inside the vehicle
- In the Kherson region of southern Ukraine a family of five was killed by Russian soldiers at a checkpoint, according to relatives
2: Cutting off basic services
Water is the most basic of human necessities and there is evidence of deliberate Russian targeting of the supply in Chernihiv.
A pumping station on the outskirts of the city was hit on 14 March.
The attack badly damaged a water reservoir and destroyed a control room, according to the head of the water company in Chernihiv, Serhiy Malyavko, who said a worker at the plant - along with three family members - were killed. The family was sheltering there after their home was destroyed by shelling.
Satellite imagery shows the damage to the plant, located by Twitter user @obretix in a forested area far away from other buildings.
Photos released by the water company showed a severely damaged treatment tank with small craters in the ground. Damage that looks like shrapnel holes pepper the buildings.
The sequence of craters visible in a satellite image suggests ground-launched strikes, says Wim Zwijnenburg, an arms researcher at Pax, a Dutch peace organisation.
"The shrapnel impact and blast direction seem to indicate the missiles were fired from the west of the water facility, [which] corresponds with the presence of Russian troop movements located to the west, according to public data on their locations."
Without access to the site itself, the experts we've spoken to say it's not possible to be precise about the weapons used. Rather than missiles, the damage may have been caused by heavy guns or mortars.
The head of the water company says the site was struck three days in a row.
"There was no military target. I'm 100% sure that the Russian troops have been destroying the city's infrastructure so that there would be no gas, no electricity or water supply in the city," Mr Malyavko told BBC News.
He said two other facilities elsewhere were also destroyed, cutting off water to most of the city's population.
The rules of war ban premeditated attacks on targets indispensable to civilian life, such as water supplies.
"This has been done to make the population panic," says Mr Malyavko. "And Russia is probably hoping that if there's a humanitarian catastrophe, the local authorities will agree to start negotiations - and that the city will surrender."
Attacks on water elsewhere
- Mariupol City Council says Russian forces intentionally targeted pumping stations and the main water pipeline from a reservoir there
- The Ukrainian government has reported severe damage to several other water utilities and waste-treatment plants across the country
3: Denial of responsibility
It was the morning of 16 March, and Ukrainian journalist Alina Klimenko received news of a much-needed bread delivery to the city. Her father, Vitalii, dashed to join the queue.
But after a short while he moved away as a nearby house came under fire. Others, now used to the sound of shelling in the city, stayed.
And then the queue itself was hit.
Alina ran out to film the aftermath. Her footage showed bodies on the ground and an ambulance racing to the scene.
At least 14 civilians died, according to Ukrainian authorities.
We have confirmed the authenticity of Alina's video and located it to a residential area in the city.
Alina's father, who has a military background, says the incoming fire was from the north-east, consistent with the attack being launched by Russian units operating several kilometres to the north of Chernihiv, according to the mapping team at the Institute for the Study of War (ISW).
Weapons expert Mark Cancian looked at the BBC's research. He said the damage was consistent with the impact of a missile with a range of up to 30km (19 miles).
A satellite image from 16 March shows Russian forces with this kind of weaponry 14km north-east of the city.
The US Embassy in Kyiv initially wrongly reported that Russian forces in the city had shot dead the civilians.
This was quickly denied by Moscow who said no Russian troops were present in the city. But the Russians went further, saying the event had either been staged, or that those killed were victims of "Ukrainian nationalists".
There have been numerous examples of this type of denial from the Russian government.
Russian denial of responsibility elsewhere
- Russian Foreign Minister Sergei Lavrov claimed that footage of bodies in Bucha was "staged" after the Russians withdrew. Satellite images contradicted this and the BBC debunked various other claims made by Russian officials
- The Russian embassy in London falsely claimed that the bombing of a maternity hospital in Mariupol in March was staged. The BBC found evidence to disprove their claims
- An estimated 300 people were killed in an attack on a theatre sheltering civilians in Mariupol. Russia has denied carrying out the attack, which has been widely condemned
Evidence of war crimes?
A critical factor in any prosecution for war crimes is obtaining clear evidence of a deliberate intent to target civilians.
Images and eye-witness statements can be the starting point, says Prof Alex Whiting, a former investigations co-ordinator at the International Criminal Court.
But investigators would then need to tackle a series of basic questions:
- Is there any way these targets could have been perceived to be military?
- Were there any military targets in the area?
- Could the targeting have been based on faulty intelligence or even down to a weapons mistake?
Throughout the conflict, the Ukrainian intelligence services have been releasing allegedly intercepted communications between Russian forces.
In one, a man with a Russian accent can be heard being ordered to shoot at a civilian car.
The authenticity of these conversations has not been verified by the BBC.
But by building a picture of consistent patterns of behaviour, the case for prosecution becomes stronger.
Sareta Ashraph, an expert in human-rights law, says investigators would be looking to establish these patterns of behaviour across the country - whether water facilities, hospitals or supermarkets had been regularly hit - in order to build up a picture of military strategy.
"This can show evidence of deliberate targeting, where the intent to bring the civilian population to its knees becomes much clearer," she says.
As the war continues, Ms Ashraph says she's reminded of Russian tactics in previous conflicts.
"I would say that Russia's actions in Ukraine contain some quite dark echoes of actions in Syria," she said.
We contacted the Russian defence ministry about all of the cases documented in this article. We have not yet received a response.