'Good man' is a comprehensive, all things considered judgement or assessment. I'm not sure that this is possible on the slender data supplied.
Suppose the doctor saved a great many lives in his professional capacity, but only because as a member of a team he could not avoid doing so (he would much rather have let the patients die or actually killed them) and his murders inflict suffering for his/ her personal pleasure. This is hardly the picture of a good man.
But the situation could be different. The doctor might be totally dedicated to saving the lives of patients wherever possible and murder purely when he morally considered mercy killing to be justified or even required in the interests of alleviating suffering. It would not be totally implausible to describe such a doctor as a good man. (He might have an erroneous conscience in the case of mercy killing but that bare fact would not make him a bad man. There is moral virtue in following one's conscience.)
So I think the judgement swings one way or another depending on the circumstances : 'circumstances alter cases'. We would need more data about the doctor than the question provides.