Is Capital Punishment Ethical?

Western democracies such as the United States still practice capital punishment for serious offenses such as treason, rape, severe murder cases, espionage, and aircraft hijacking which lead to murder. Capital punishment can be defined as the act of executing an individual by the government as a punishment for a particular crime following a legal trial. The methods used in executing the offenders include electrocution, lethal injection, firing squad and hanging. Death Penalty information centers (2017) states that twenty people in the US were executed in 2016 the number is the lowest since 1991.  What are the several arguments about the ethics of capital punishments where some support the practice while others are against it?