Surveillance video captured the moment the men, who include a 68-year-old grandfather, were shot outside a vehicle dealership.
The video, obtained by CNN, is reportedly being investigated by Ukrainian prosecutors as a potential war crime.
Security cameras filmed the moment on March 16 when Russia’s forces tried to capture the capital Kyiv in the early stages of country’s invasion.
They appear to show five Russian soldiers arriving at a campervan dealership before trying to break into the premises by firing at locks and smashing glass.
The owner approaches and with hands raised and is stopped and apparently searched for weapons.
The other victim, identified as Leonid Oleksiyovych Plyats, 68, a security guard, arrives and is also frisked.
They appear to have a conservation before both the soldiers and civilians walk away.
At least two of the attackers are then seen coming up behind the men and opening fire. Both the victims collapse to the floor.
But, as the soldiers are seen inside the dealership removing their body armour and ransacking the property, the grandfather tries to save himself.
Video shows him struggling to his feet before tying what looks like a tourniquet around his thigh.
CCTV footage then shows Mr Plyats dragging himself into the building to contact the local territorial defence group.
The volunteers arrived and opened fire on the soldiers, forcing them back into their vehicles, but were outgunned and had to retreat,
But the grandfather died before he could be reached by the volunteers.
One of the would-be rescuers told CNN the soldiers had asked the civilians for cigarettes before shooting them in the back.
The dead grandfather’s daughter, Yulia, told the broadcaster: “They are executioners.
“It’s awful because my father was a civilian, he was 68, a peaceful unarmed man.”
“They need to be judged,” she said of his killers. “I hope for an international court. I hope that not only Ukraine but the whole world will learn about their crimes.”
The footage emerged as Ukraine announced the first Russian to stand trial for committing war crimes in the war-torn country.
More than 10,700 crimes have been registered since the start of the war, Ukraine’s prosecutor general Iryna Venediktova said.
Vadim Shishimarin, 21, is accused of killing a 62-year-old civilian on February 28.
Shishimarin and four other soldiers were fleeing in a stolen car outside the village of Chupakhivka before the accused was ordered to shoot the civilian so he could not report them.
The US and the UK have also accused Russia of committing war crimes since the invasion began in February.
The UK announced a team of experts would be dispatched to assess the alleged atrocities committed by Russian troops earlier this month.
Attorney General Suella Braverman also led a group of war crimes experts in Poland as part of the UK’s support for investigations into Russian atrocities.