When you are discussing the death penalty, a single case chosen for its specific emotional appeal means nothing whatsoever. Do not depart from the big picture. Excluding war and euthenasia, killing should always, always, be regarded as taboo which once passed carries extreme circumstances for the perpetrators, thats exactly why we can't have society doing it. It breeds disrespect for life, and violence.
As for the pedophiles, send them off to a deserted island or something. Murder, however, should not be in the purview of society.