Simple: You kill, you get killed. It's very fair. Although I do think that the electric chair is too much. The killer suffers more. Execution should be completely painless, an immediate death.
Don't you think you might be oversimplifying things? Following your logic, all war heroes deserve to be executed. When it comes to determining the life/death of an individual many factors must be considered.
Not all killings are exactly the same, hence shouldn't be deemed as equal. Some are much more brutal and wicked, while some may be compassionate and just. A murderer who tortures their victims is given in return a painless death,while the victim faced a merciless one. Somehow I don't see the fairness in that. If your idea of justice is to give the criminal what they deserve, shouldn't the criminal instead have a taste of their own medicine?
I haven't researched enough to form a strong stance, but currently I remain against it. I'll probably get into reasons later.