Agreed...if she's guilty (and I suspect she was at least somewhat involved.) However, the exact nature of her involvement is not known to us now...
Only a prosecuter that is worthless would allow these two cases to be linked. Nail him to the wall under the letter of the wall and deal with her likewise. In a separate trial. IN no way does her consent change his liability before the law. IT is kidnapping if a child leaves the guardianship of a parent without the parents consent. He killed them because they did not give their consent.