I shall try to put such an awful thing delicately.
He was sentenced to life for murder, not rape.
The sentence guidelines for the single rape of a child under 13 is 10 years; the range is 8-13 years in custody.
At the time of the offence the sentence guidelines for murder was 22 years (now 25 years).
A whole life tariff can be given in certain circumstances. The only applicable circumstance to this case is 'sexual motivation'.
The evidence indicates that he murdered to cover up the rape, not for sexual kicks.
So, the judge has applied the law in the same way as any other judge would.