It's a tempting thought, given high profile killers like him otherwise cost more to board and protect than the fees at a top public school. Much good could be done spending the money on those in need but the Bleeding Heart Brigade will never allow the death penalty to be re-introduced, however heinous the crime.
I'm less than convinced being 'civilised' means being lenient towards calculating, cold-bloodied killers and indiscriminate, mass murderers. As regards your particular point - yes, if ever re-introduced, past cases should be reviewed and the penalty imposed where appropriate.
All sorts of bogus 'human rights' arguments are advanced on behalf of evildoers, with little or no regard to rights of victims and their relatives.
I'd be more than ready to give Huntley the good/bad news - AND the lethal injection.