You are correct. The opinion that all 10 commandments are the basis of US law is wrong. And Hebrew misinterpretation is part of the issue. Number six is exactly, 'thou shalt not murder'. Therefore, a society can kill for the good of society. The death penalty is a reasonable punishment, but is excluded in many part of the US.

I disagree with this part, but only because I don't believe death should be warranted without incontrovertible evidence and a confession. The chance of putting an innocent man to death is more abhorrent to me than letting a killer live.

I agree. Incontrovertable evidence, but not a confession. Confessions can be coerced.