John Jonchurk was arrested after throwing his 5-year-old child Phoebe 60ft from the bridge in Tampa Bay, killing her.
Rescuers found the child 40 minutes after she was thrown, but she could not be resuscitated. She was still strapped into her car seat.
Jonchuck’s mother has now said she never wants to see her son again, adding that she wishes he’d killed himself rather than her granddaughter.
‘I don’t forgive him. There is no sense in this. He didn’t have to do this to her. I just wish there was one thing God could do was to bring her back,’ said the 51-year-old.
The girl’s mother Michelle Kerr, who was only given restricted access to Phoebe by her father, last saw her child on Christmas Eve and described her as ‘my angel.’
Michelle and John had previously been involved in a tumultuous relationship, during which the police were called several times on domestic abuse allegations.
John has been diagnosed as bipolar according to Kerr, and was ‘not mentally stable.’
The officer who witness John throwing Phoebe from the bridge reported that he heard her scream as she fell.
He has been charged with first degree murder.