KYIV, Ukraine >> A 21-year-old Russian soldier facing the first war crimes trial since Moscow invaded Ukraine pleaded guilty today to killing an unarmed civilian.

Sgt. Vadim Shishimarin could get life in prison for shooting a a 62-year-old Ukrainian man in the head through an open car window in the northeastern Sumy region on Feb. 28, four days into the invasion.

Shishimarin, a captured member of a Russian tank unit, was prosecuted under a section of the Ukrainian criminal code that addresses the laws and customs of war.

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.

It was not immediately clear how many of the suspects are in Ukrainian hands and how many would be tried in absentia.

Prosecutors plan to continue presenting evidence against Shishimarin following his guilty plea, although the trial is like to be shorter.

As the inaugural war-crimes case in Ukraine, Shishimarin’s prosecution was being watched closely. Investigators have been collecting evidence of possible war crimes to bring before the International Criminal Court in The Hague.

Venediktova’s office has said it was looking into more than 10,700 potential war crimes involving more than 600 suspects, including Russian soldiers and government officials.

With help from foreign experts, prosecutors are investigating allegations that Russian troops violated Ukrainian and international law by killing, torturing and abusing possibly thousands of Ukrainian civilians.

Shishimarin’s trial opened Friday, when he made a brief court appearance while lawyers and judges discussed prosecedural matters. After his plea today, the proceedings were continued until Thursday, when the trial is expecgted to resume in a large courtroom to accomodate more journalists.

Ukrainian authorities posted a few details on social media last week from their investigation in his case.

Shishimarin was among a group of Russian troops that fled Ukrainian forces on Feb. 28, according to Venediktova’s Facebook account. The Russians allegedly fired at a private car and seized the vehicle, then drove to Chupakhivka, a village about 200 miles east of Kyiv.

On the way, the prosecutor-general alleged, the Russian soldiers saw a man walking on the sidewalk and talking on his phone. Shyshimarin was ordered to kill the man so he wouldn’t be able to report them to Ukrainian military authorities. Venediktova did not identify who gave the order.

Shyshimarin fired his Kalashnikov rifle through the open window and hit the victim in the head, Venediktova wrote.

“The man died on the spot just a few dozen meters from his house,” she said.

The Security Service of Ukraine, known as the SBU, posted a short video on May 4 of Shyshimarin speaking in front of camera and briefly describing how he shot the man. The SBU described the video as “one of the first confessions of the enemy invaders.”

“I was ordered to shoot,” Shyshimarin said. “I shot one (round) at him. He falls. And we kept on going.”

Russia is believed to be preparing war crime trials for Ukrainian soldiers.