? Re-Michigan Law/Rights for the unwed dad for a premature baby born & Missing!?

My son & his girlfriend were expecting a child. As of about 6 days ago, the girlfriend is no longer pregnant. She led us to believe the baby was at a nearby hospital, however, we called and they claimed she had not been there. On day 4 she said the baby actually died. First she said at birth, last night she said she miscarried 6 weeks ago. We do know she was 'for sure' pregnant 3 weeks ago, Mother's Day and at least 1 1/2 weeks ago. Can we get a subpoena to force her to show proof of babies whereabouts so we can prove paternity? Any additional advise or comments would be GREATLY appreciated. We are dying to find out anything on our little missing daughter/granddaughter.