Seriously, I don't consider this being any special risk, because if a child rapist rapes or kills a kid, he needs to be caught or will do it again, this or that way, and I simply see no reason to keep such an individual alive, which, like in this case, will do it again and did so much harm to other individuals and the group as a whole.The risk of such a policy is that it gives the rapist a motive to murder the kid.
If he murders one kid and we get and eliminate him, many others will still be save - that argument is no argument to me, as it would mean to be lenient just for letting a paedophile raping children and not killing them, if he is in the right mood of course and has no murderer-tendency anyway.
On the long run the whole issue will be solved by knowing the reasons for the aberrant and dangerous behaviour and eliminting them - with Eugenic and Euphenic measures.
If someone would rape a child of mine, death penalty would be the only punishment which would satisfy me - probably - but at least more than any other punishment.
And one thing is for sure, I wouldn't want to see that guy around - no matter what and to know he's dead, as an example for others and to wash away the shame - such a shame can only be washed away with blood. That my child would ever see that guy around, in freedom, is simply inacceptable.
In such cases I stick to the good old clan rules - no mercy for those who harmed my kin out of such low motives, and his kin should be glad if being left alone...
Those defects must be erradicated, it is about the elimination of this dangerous defect, nothing else on the long run, which is the only way to prevent/reduce such incidences in the future.
Because people which want to have sex, even forced one, with REAL MINORS, I'm not speaking about young ones, but those which are not even close to sexual maturation, have a general problem, they can be treated for free, if admitting their problem, or they can be punished if doing a crime and future research will find out the cause and help to get rid of it in our genpool and culture.