I strongly agree that prison isn't the only option. At the same time, I can't support the notion that Charles Manson, Timothy McVeigh, Dylann Roof, and Dzhokhar Tsarnaev should all be free men today.
Be that as it may, and maybe they shouldn’t be free. But I don’t think they should be in prison either. You can have your freedom punitively stripped away from you without being held in prison.
The problem with capitol punishment is that it's irrevocable. Even though we know these people committed these heinous crimes, there's going to be a line for where it's not ok to sentence someone to death because the proof is not airtight. When cases are close to that line, there's always the chance that they weren't actually guilty. I believe this will be the case no matter where that line is.
Prison is not the only option by a long shot.