A man who raped a 12-year-old girl who later gave birth to his baby has been awarded joint legal custody of the pair's eight-year-old child, according to the victim's attorney.

Christopher Mirasolo was jailed in 2008 for the horrific sexual assault of a child in Michigan, says the victim's lawyer.

After negotiating a plea bargain he was jailed for attempted third-degree criminal sexual conduct and served under a year in prison, released early to care for his sick mother.

And he was later convicted of a further sexual assault on another victim between the ages of 13 and 15 years old, serving four years before being released in 2014.

Now, according to Rebecca Kiessling, the victim's attorney, the 27-year-old rapist was awarded the custody rights after a DNA test confirmed he was the father, The Detroit News reported.

Incredibly the legal custody, awarded by Judge Gregory S. Ross, also included the requirement that she needed to move from Florida back to Michigan so that Mirasolo, from Brown City, could be near the child.

"This is insane," said Kiessling, who filed objections Friday with the judge. "Nothing has been right about this since it was originally investigated.

"He was never properly charged and should still be sitting behind bars somewhere, but the system is victimizing my client, who was a child herself when this all happened."

The case is believed to be the first of its type in the state and possibly throughout the US with Kiessling seeking protection under the federal Rape Survivor Child Custody Act.

"The Judge also restricted the child's domicile and residence, disclosed the rape victim's home address to her rapist, and ordered his name on the birth certificate — all without the mother's consent or any opportunity to be heard," Kiessling added.

The attorney believes that the court decision follows an investigation into child support money that has been claimed by the victim in the past year.

Kiessling told The Detroit News that Mirasolo forcibly raped and threatened to kill her client and her 13-year-old sister and another friend, holding them captive for two days.

Mirasolo's attorney Barbara Yockey, said her client "never initiated this" and the motion by the court was just routine procedure.

"I don't know what his plans or intentions might be regarding any future relationship with the child," Yockey said.

"This might be something we will have a conversation about, but he has not been served with any other court papers and is not scheduled to be in court."

A hearing is scheduled for 25 October.