Why didn't Walton kill the creature?

Walton regards the creature with a mixture of curiosity and compassion, but cannot bring himself to console him. The creature says that it caused him agony to commit his crimes, since his heart "was fashioned to be susceptible to love and sympathy"; only the greatness of his misery drove him to vice and hatred. Walton, though he is touched by the creature's remorse, still feels great indignation at his crimes: he says that the creature has "thrown a torch into a pile of buildings, and when they were consumed...sat among the ruins and lamented the fall." Walton still can't bring himself to comit murder.

Walton believes the creature when it says that it will burn itself up in the middle of the Arctic and die.