Why was Trofin Zhdanko's sentence of death commuted in the novel, Alaska?

Trofin Zhdanko had killed the governor in Eastern Siberia and was sentenced to be hanged. He was taken to Vologda and imprisoned, where he Tsar came to see Trofin, whom he knew and trusted. The Tsar gave him his freedom. Trofin was twenty-two years of age at the time. The Tsar wanted him to find a good captain, travel to Siberia, build a ship and explore the northern waters.