copycat killer

Translations
подражающий убийца
The detective suspected that the new murder was the work of a copycat killer.
Детектив подозревал, что новое убийство было делом рук подражающего убийцы.
Definitions
A copycat killer is a person who commits a crime, especially a murder, that closely imitates or is inspired by the methods or motives of another well-known criminal or crime, often seeking similar attention or notoriety.
Words
copycat

noun
подражатель
killer

noun
убийца