由死刑改判无期徒刑: commute the death sentence to life imprisonment
这个主犯被判无期徒刑: the principal criminal was sentenced to life imprisonment
判处: sentence; condemn 短语和例子判处 5年徒刑 sentence sb. to five years' imprisonment; 被判处流刑 be condemned to exile; 他被判处死刑。he was sentenced to death. 他被判处无期徒刑。he was condemned to life imprisonment