How can a father get visitation rights to his child?

I’m asking for a friend of mine who is from Saudi Arabia. His wife is Puerto Rican and they were living with their son in Phoenix. The wife left to go back to Saudi to visit family and has not returned to the U.S. My friend has not seen his son in 6 months. The wife refuses to tell him where exactly she is. What does he need to do to force her to come back so he can see his son? Can she be held criminally responsible for kidnapping and full custody awarded to him? He is a good father and she had no reason to take his child away.