Hate to say I'm for the death penalty but... definitely in the cases of mass murder or multiple murder, or contract killings, the person who does it should be executed. As to juveniles, if they commit the crime, and if we are talking about a male at least 15 years old (or possibily 14) then execute him. Hanging preferred. And if a 15 year old commits the crime he should preferably be executed while still a teenager. Juvenile females??? Really prefer not to go there, but...
BTW, no lethal injection. That's simply too sterile. I want the gallows or a firing squad to be used. The gas chamber if both chairs are being used (the chamber has two chairs for the possibility of a double). Preferrably the condemned being a man in his teens or twenties, athletic, well built. And guilty. And I don't want a quick hanging. I want him still to be alive if you cut him down after 10, 15 minutes of swinging.