When Leonid Pliats and his boss were shot in the back by Russian soldiers, the killing was captured on CCTV cameras in clear and terrible detail.

The footage, which was obtained by the BBC, is now being investigated by Ukrainian prosecutors as a suspected war crime.

It was the height of the fighting around Kyiv and the main roads into the capital were a battlefield, including around the bicycle shop where Leonid worked as a security guard.

But this was no firefight: the video clearly shows five heavily armed Russian soldiers shooting the two unarmed Ukrainians and then looting the business.

We have pieced together the full sequence of events, matching what was recorded on multiple CCTV cameras around the site with the testimony of people Leonid phoned that day, as well as the Ukrainian volunteer fighters who tried to rescue him.

The Russians arrive in a stolen van daubed with the V sign used by Russian forces and the words Tank Spetsnaz in black paint. They wear Russian military uniform and approach with their guns up, fingers on the triggers.

Leonid walks towards the soldiers with his hands up to show he's unarmed and no threat.

The Russians initially talk to him and his boss through the fence. There is no audio on the footage but the men seem calm, they even smoke. Then the Ukrainians turn away and the soldiers start to leave.

Suddenly they turn back, crouch then shoot the two men multiple times in their backs.

One is killed outright but somehow Leonid manages to stagger to his feet. He even ties his belt around his thigh to slow the blood, then stumbles to his cabin where he begins to call for help.

Vasyl Podlevskyi spoke to his friend twice that day, as he sat bleeding heavily.

Leonid told him the soldiers claimed they don't kill civilians, then they shot him.

"I said can you at least bandage yourself up? And he told me, Vasya, I barely crawled here. Everything hurts so much. I feel really bad," Vasyl remembers the call.

"So I told him to hang in there and started phoning the territorial defence."

The men he called used to sell air conditioning before the war.

Now volunteer fighters, Sasha and Kostya show me video on their mobile phones of Russian tanks rolling past their positions. Their job was to send real-time information on Russian movements to Ukraine's military positions up the road.

When Leonid Pliats was injured they were tasked with crossing the dangerous E40 highway to try to save him. Even today, the road is littered with the burned-out carcasses of Russian tanks, a reminder of the intensity of the fighting.

As the security guard lay bleeding, Russian troops were still on site.

On the CCTV you see them shooting their way into rooms, stealing bicycles and even a scooter and lolling around in the director's office, drinking his whisky, and rifling through his cupboards.

Outnumbered and only lightly armed, Sasha and Kostya were forced to wait although they realised that Leonid was dying.

"We talked to him on the phone, we tried to calm him. We told him, it's ok. Everything will be ok. You'll survive," Sasha tells me they did their best to comfort him.

"We said we were on our way. Maybe that helped him. Maybe. But unfortunately, by the time we made it, he was dead."

Even as they collected the two men's bodies, the volunteer fighters had to take cover as a Russian tank rolled past.

There is ample evidence against the men responsible for these killings. We have studied the video in minute detail and the Russian soldier who we believe was one of the killers is clearly visible, his face uncovered.

It is a long time before his friends realise they are being filmed and smash one of the security cameras.

We showed the footage to the chief of police for Kyiv region and he told us the bodies of 37 civilians, all of them shot dead, were found along the road to Ukraine's capital after Russian forces were pushed back.

The Prosecutor's office confirms that it is now investigating the killing of Leonid and his colleague as a possible war crime: one of more than 10,000 cases they have registered.

"My Dad was not a military man at all. He was a pensioner. They killed a 65-year-old. What for?" Leonid's daughter, Yulia Androshchuk, wants to know.

She is abroad and hasn't even been able to bury her father yet because of the war.

"I'm not so much furious as full of grief - and fear. These damn Russians are so out of control, I'm afraid of what they might do next," she told me.

Yulia hopes those responsible will stand trial someday, somehow. For now, she wants people to know exactly what happened to her father and for the brutality to stop.