Again, I don't have enough information to make a judgement about this case. I think it is unfortunate that either parent should be denied access to their child, and it is selfish of either parent to take their child away, but who knows what goes on in a family. And I don't know what kind of a father the Swiss father was or what kind of a mother the American mother was, or if it was possible for the American mother to remain in Switzerland, etc.
Generally, if all things are otherwise equal, I think the child belongs with the mother. But I think it is the responsibility of both parents to make the child accessible to the other parent, to cooperate as much as possible with the other parent, and to promote a good relationship between the other parent and the child/children.