The first trial of a Russian soldier for war crimes in Ukraine since the invasion concluded Monday with Sgt. Vadim Shishimarin, a 21-year-old from Siberia, found guilty of premeditated murder and violating international laws for war.

Shishimarin was given a life sentence.

The three-judge panel determined that Shishimarin, a captured Russian tank-unit sergeant, fatally shot Oleksandr Shelipov, a 62-year-old civilian man in the head in late February.

Shishimarin’s defense had argued for an acquittal, saying his client was carrying out what he perceived to be a direct order that he initially disobeyed. He had pleaded guilty and asked Shelipov’s widow for forgiveness.

During the trial the court heard that Shishimarin was ordered to kill the man so he wouldn’t be able to report them to Ukrainian military authorities. Shishimarin fired his Kalashnikov rifle at the victim through the open window of a car.

“I was nervous about what was going on. I didn’t want to kill,” Shishimarin said as the trial ended Friday in Ukraine’s capital Kyiv.

Ukrainian Prosecutor General Iryna Venediktova previously said her office was readying war crimes cases against 41 Russian soldiers for offenses that included bombing civilian infrastructure, killing civilians, rape and looting. Venediktova’s office has collected more than 10,700 allegations of war crimes against Russia involving more than 600 suspects, including Russian soldiers and government officials.

Ex-Defense Secretary: Russia unlikely to use nuclear weapons

Even with the war in Ukraine going much worse than expected for Russia, the probability of Russian President Vladimir Putin deploying a nuclear weapon is “low but not zero,” former U.S. Secretary of Defense and CIA Director Robert Gates said Sunday.

Speaking on CBS’s “Face the Nation with Margaret Brennan,” Gates said Russia’s use of a tactical weapon would prompt a strong response from the West, including establishing a no-fly zone over Ukrainian skies. In addition, he said such a move wouldn’t “change the military equation on the ground” because Ukrainian forces are spread widely and are fierce in their resistance.