There are a few references to POW killings on the Russian side, and Alexander Figner, commanding one of the flying detachments, was notorious for his atrocities against the Allied forces in 1812. Denis Davydov, who knew Figner (who tried to assassinate Napoleon in the Kremlin) quite well, left an interesting account of him:
"I had long heard about the barbarity of [Figner] but could not believe that it could extend to killing unarmed enemy combatants, especially at the time when circumstances had changed in our favor, and it seemed that lowly feelings, and especially that of revenge, had no place in our hearts that were filled with powerful and complete feelings of joy! But as soon as he learned about my prisoners, he rushed to me begging to let his new Cossacks to tear them apart [rasterzat, with Davydov's emphasis] since as, he told me, his Cossacks were not yet stirred up [natravleny]...
[Disgusted, Davydov refused and tried to persuade Figner against it]. He told me, "Do not tell me you were not executing?" I replied, "I did execute two traitors, one of whom had robbed the church." "But you also executed prisoners, right?" - [Davydov responded] "Lord save me from that! You can even secretly inquiry among my Cossacks [who would confirm this.]" [Davydov then again condemned Figner for killings]
"We then fell silent. Concerned that he might kidnap my prisoners at night, I, under pretext of giving orders to my troops, left the hut and doubled the guards... and then sent off the prisoners to the headquarters at dawn.
We often talked about Figner - this strange man, who left a bloody trail among the men like a meteor destructing everything in its path. I could not understand his thirst for killing! [I would probably somehow understood it] if he were turning to killings in critical circumstances, surrounded by enemy corps, isolated and hard pressed by the enemy detachments and unable to get his prisoners to the army. Yet, he usually put them to death not at the time of danger but after it had already passed.
His barbarity also hurt his Machiavellian designs since it destroyed the live evidence of his exploits. We knew that he was always very precise in his reports and that he indeed [often] seized and executed [istreblyal] three or four hundred rank-and-file and senior ranks. However, outside people, officials in the army and the headquarters always doubted his successes and assumed that his exploits were only on paper and not in reality. In addition to all of this, his behavior also deprived him of the best of his officers, who were initially faithful to him. They had shuddered at not only becoming his accomplices but even witnessing these wanton bloodsheds and abandoned him with one man - NCO Shianov of the Akhtyrsk Hussar Regiment, a fearless but bloodthirsty man, who, due to his utter ignorance, sought to get to the Heavens by exterminating the enemy by all means possible..."