The number of prisoners serving lifesentences has fallen.
被判无期徒刑的囚犯数目下降了。
《牛津词典》
2
Some were serving lifesentences for murder.
有些人因为谋杀罪在服无期徒刑。
《柯林斯英汉双解大词典》
3
Some legislators advocate mandating a sentence of life in prison for anyone who, having twice served sentences for serious crimes, is subsequently convicted of a third serious crime.