Vadim Shishmarin, 21, is back in court, one day after he pleading guilty to killing a 62-year-old Ukrainian civilian just days into the conflict.

Shishmarin confessed to the killing Thursday morning.

The widow of the victim testified in court that her husband meant everything to her, and she thinks the Russian soldier deserves life in prison, but if he gets exchanged for any of the Azovstal defenders she wouldn’t object.

"I feel very sorry for him," she said. "But for a crime like that -- I can't forgive him."

Shishimarin could spend the rest of his life in prison.

-ABC News' Joe Simonetti

Mass shelling of the Sumy region continued from Russian territory Wednesday evening, said Dmytro Zhyvytskyy, the governor of Sumy, on Telegram.

The shelling was along the entire border between the Sumy region and Russia, according to Zhyvytskyy.

Zhyvytskyy said Ukraine responded to the shelling appropriately and no casualties were reported.

-ABC News' Joe Simonetti

Mykhaylo Podolyak, an adviser to Ukrainian President Volodymyr Zelenskyy, told Russia not to offer Ukraine a cease-fire, because it would be impossible without Russian troops' withdrawal.

"Ukraine is not interested in new 'Minsk' and the war renewal in a few years," Podolyak said in a tweet, referring to the capital of Belarus and that country's allegiance to Russia. "Until [Russia] is ready to fully liberate occupied territories, our negotiating team is weapons, sanctions and money."

-ABC News' Joe Simonetti

The International Committee of the Red Cross said Thursday that it has registered hundreds of Ukrainian prisoners of war from a besieged steel plant in war-ravaged Mariupol this week, after the Ukrainian city fell into Russian hands.

A team from the ICRC began on Tuesday to register combatants leaving the Azovstal Iron and Steel Works plant, including the wounded, at the request of the parties to the conflict. The operation continued Wednesday and was still ongoing Thursday. The ICRC is not transporting prisoners of war to the places where they are held, according to a press release from the organization.

"The registration process that the ICRC facilitated involves the individual filling out a form with personal details like name, date of birth and closest relative," the organization said. "This information allows the ICRC to track those who have been captured and help them keep in touch with their families."

The Geneva-based humanitarian agency, which has been working in Ukraine since 2014, noted that it "maintains a confidential dialogue with the parties to the conflict on their obligations under international humanitarian law."

"In accordance with the mandate given to the ICRC by States under the 1949 Geneva Conventions, the ICRC must have immediate access to all POWs in all places where they are held," the organization added. "The ICRC must be allowed to interview prisoners of war without witnesses, and the duration and frequency of these visits should not be unduly restricted. Whenever circumstances permit, each party to the conflict must take all possible measures to search for and collect the dead."

For weeks, Ukrainian fighters and civilians were holed up inside Mariupol's vast Azovstal plant as the remaining pocket of Ukrainian resistance to Russia's relentless bombardment of the strategic southeastern port city. Russia claimed Thursday that 1,730 Ukrainian fighters had surrendered in Mariupol over the previous three days, while Ukraine confirmed Tuesday that more than 250 had yielded in the initial hours after it ordered them to do so.

Mariupol is the largest city that Russian forces have seized since launching an invasion of neighboring Ukraine on Feb. 24. Its complete capture gives Russia total control of the coast of the Sea of Azov as well as a continuous stretch of territory along eastern and southern Ukraine.

-ABC News' Max Uzol

White House national security advisor Jake Sullivan hinted Thursday of more sanctions coming against Russia in the "next week or two" aimed at targeting ways Moscow is evading sanctions already imposed.

“Where our focus will be over the course of the coming days is on evasion,” Sullivan said Thursday at the Economic Club of Washington. “As Russia tries to adjust to the fact that it’s under this massive economic pressure, what steps do they take to try to evade our sanctions and how do we crack down on that? And I think we'll have some announcements in the next week or two that identify targets that are trying to facilitate that evasion both inside Russia and beyond."

When Sullivan was asked whether sanctions will automatically be lifted if a negotiated peace deal between Russia and Ukraine is worked out, he appeared cautious with his words, saying, “a lot of that depends on what the shape and scope” of the agreement is.

“A lot of it depends on what the Ukrainians, in consultation with us and the Europeans come to agree to," Sullivan said. "You know, we're not going to do a deal over the head of the Ukrainians where we give a bunch of sanctions relief to Russia. But if some measure of sanctions relief were built in to some credible diplomatic solution led by the Ukrainians, that's something that we would happily discuss."

But Sullivan said Russian oligarchs shouldn't expect to ever get back their yachts and other assets seized under sanctions that have been imposed, saying the ultimate goal is "not to give them back” once the war is over.

“The president is actively looking at how we can deal with the fact that as we seize these assets, our goal is not to give them back. Our goal is to put them to a better use than that," Sullivan said. "But I'll be careful in what I say today because there's an ongoing kind of policy process around how we end up dealing with that question. But, rest assured, that the goal is not just to sit on them for a while."

-ABC News' Justin Gomez