Vadim Shishimarin shot dead Oleksandr Shelipov as he rode his bicycle in village in Sumy region during early days of invasion

A court in Kyiv has sentenced a Russian soldier to life in prison for the killing of a Ukrainian civilian, in the first verdict in a trial related to war crimes carried out by the Russian army during its invasion of Ukraine.

Vadim Shishimarin, a 21-year-old sergeant, was found guilty of killing 62-year-old Oleksandr Shelipov in the Sumy region during the first days of the invasion.

The verdict was delivered on Monday by the judge Serhii Ahafonov in a packed courtroom, with dozens of Ukrainian and foreign television cameras crammed into the small chamber.

The judge said although Shishimarin cooperated with the investigation and expressed remorse, the court could not accept his claim he did not mean to kill Shelipov when he fired at him. “The murder was committed with direct intent,” he said.

Shishimarin, wearing a grey and blue hoodie, listened to the judge deliver his long verdict with his head bowed from inside the glass box for defendants. He was given a translation of the judge’s words from Ukrainian to Russian by a court-appointed translator.

Shishimarin was commanding a tank division from the Moscow region that came under attack on 28 February, prosecutors said. The attack led the Russian soldiers to disperse and Shishimarin ended up stealing a car with four other soldiers.

When they saw Shelipov riding a bicycle and speaking on his mobile phone, one of the other soldiers told Shishimarin to shoot him, for fear he would give away their positions. Shishimarin fired three or four shots at Shelipov from his Kalashnikov.

“I was ordered to shoot, so I opened fire on him and he fell. We carried on driving,” he said in a video interrogation released by Ukraine’s SBU security services.

Shishimarin pleaded guilty to the crime, but his lawyer argued that his client was following an order and did not have intent to kill. Shishimarin also apologised to the wife of the victim.

“The court cannot recognise the sincerity of his repentance,” Ahafonov said in his verdict.

Shishimarin was whisked away from the court after the hearing in the back of a police van. He has 30 days to launch an appeal.

Speaking outside the courthouse, Shishimarin’s lawyer, Viktor Ovsyannikov said he would challenge the verdict. “This is the most severe sentence and any level-headed person would challenge it,” he said. He added that he believed “societal pressure” had influenced the court’s decision.

The prosecutor Andriy Syniuk said the ruling was “lawful and justified”.

It is the first in a number of war crimes cases that Ukraine prosecutors want to try as quickly as possible. Ukraine’s prosecutor general, Iryna Venediktova, has said she is preparing more than 40 cases related to war crimes that could come to trial soon, and Ukrainian authorities say they have registered more than 10,000 war crimes across the country.

Trying cases so quickly, while the conflict rages on, is extremely unusual and may violate elements of the Geneva conventions, legal experts say. However, Ukraine has made swift justice a priority, partly as a warning to Russian troops still occupying parts of the country that they may face justice for any crimes they commit.

In an interview with the Russian independent news outlet Meduza, Shishimarin’s mother, Lyubov, claimed her son was a caring and kind young man who had joined the army partly because there was a lack of opportunity in their home town, and partly to help support the family after his stepfather was killed last year.

She said her son called in late February and said: “Mummy, I won’t have a telephone for a week, I have to give it up. If someone tells you I went to Ukraine, don’t believe them.” The next she heard of him was when she found out he was a prisoner in Ukraine, she said.

Shelipov’s widow, Katerina, identified Shishimarin as the man who shot her husband during a court hearing last week, and told the court she hoped he would receive a life sentence. “But if he is traded for our defenders of Azovstal, I would not mind,” she said.

There has been some speculation that once convicted, Shishmarin and others may be used as part of an exchange for Ukrainians held by Russia, including the more than 2,000 defenders of the Azovstal steel plant in Mariupol who recently surrendered to the Russians.

Russian officials have veered between calling for harsh punishments, including even the death penalty, for some of the fighters, and suggesting they may be open to an exchange.

On Monday Denis Pushilin, the leader of Russia-backed Donetsk separatists, said there should be an “international tribunal” for the Azovstal defenders, many of whom have been called “Nazis” by Russian authorities.

“If an enemy [soldier] has laid down his arms, his future fate is decided by a court, if he is a Nazi criminal, this will be a tribunal,” Pushilin said.

The Kremlin said on Monday it was following the Shishimarin case. “Of course we are worried about the fate of our citizen. Unfortunately we have no possibilities to defend his interests there,” said Vladimir Putin’s spokesperson Dmitry Peskov on Monday. He said the Kremlin would use “other channels” to assist Shishimarin.