Sentence:  He was also at the same time gaining practical experience as a safe breaker and highwayman , and learning how to shoot to kill from a Neanderthal convicted <WSD>murderer</WSD> named Gene Geary , later committed to Chester Asylum as a homicidal maniac , but whose eyes misted with tears when the young Dion sang a ballad about an Irish mother in his clear and syrupy tenor . 
Meaning of the word marked with <WSD> tags:  a criminal who commits homicide (who performs the unlawful premeditated killing of another human being)