A 21-year-old Russian soldier was sentenced to life in prison in Kyiv on Monday for killing a Ukrainian citizen in cold blood, marking the first war crimes conviction since the invasion of Ukraine.

Sgt. Vadim Shishimarin pleaded guilty to killing 62-year-old Oleksandr Shelipov in the head barely four days into the battle in the village of Chupakhivka in the northeastern Sumy area.

Shishimarin testified last week that he was told to shoot the unarmed victim. According to him, an officer argued that Shelipov, who was on his telephone at the time, could pinpoint their whereabouts to Ukrainian forces.

Shishimarin, according to Judge Serhiy Agafonov, fired six rounds at the victim’s head with an automatic weapon while carrying out a criminal command from a higher-ranking soldier.

Shishimarin sat calmly in a reinforced glass box in the courtroom, wearing a blue and gray hooded sweatshirt, and remained stone-faced while the judgment was read out.

He stood with his head lowered for the majority of the time, listening to a translator.

When confronted by the victim’s widow, Kateryna Shelipova, who interrogated him about his intentions, the former Russian tank commander confirmed his guilt last week.

The war crimes trial is very significant for Ukraine, which has accused Russia of atrocities and cruelty against people and claims to have discovered over 10,000 potential war crimes.

Russia has denied any involvement in war crimes or targeting of people.

The Kremlin did not respond to Shishimarin’s decision right away. It has previously stated that it has no knowledge of the trial and that its capacity to help is limited due to the lack of a diplomatic post in Ukraine.

Shishimarin and four other Russian military officers stole a privately owned automobile on Feb. 28 to flee when their column was targeted by Ukrainian forces, according to Ukrainian state prosecutors. The troops drove towards Chupakhivka hamlet, where they observed Shelipov riding a bicycle while talking on his phone.