How come the european union does not use the death penalty?

The death penalty is a right form of punnishment for the most serious crimes like murder. How then can most european countries just have life imprisonment without parole as the punnishment for the most serious of crimes? I think the european union should reinstate the death penalty for all of its member states kinda of how america uses it for serious crimes over there. We still can have a great human rights record like the usa and still impose the death penalty in serious crimes commited. The european parliament should reconsider their issue on the death penalty and should pass a law having capital punishment as a legal form of punishment.