What is the ruling if paternity is established to one claimant, and then the two kill the child?

Primary text

If paternity is established to one claimant via the expert genealogists (*qaafah*), and then both kill the child, the father does not face retribution (*qisas*) for killing his own son, but the other claimant is executed for murder because he is a partner in the killing of the father's son.