For a quarter century, James Duncan has maintained his innocence, even after a judge sentenced him to 70 years in prison for beating his infant son.Now, 21 years after he was found guilty of aggravated child abuse, the father will have the opportunity to prove he wasn't responsible for his son's injuries. The 2nd District Court of Appeal on Friday granted Duncan's request for a hearing to present new evidence.The evidence, according to court records, is a "groundbreaking scientific discovery" that the defense said could prove the baby's 13 bone fractures were caused by a rare bone disease — and not the father.The son he went to prison for abusing also believes his father is not to blame."This situation that I have had to live my entire life, knowing that (my father) is in jail for something I believe he did not do, has been very hard and stressful," wrote Kody Duncan, now 24, in a letter that was part of the father's appeal.He was born on Feb. 8, 1993. When Kody was 8 weeks old, the mother noticed their child couldn't move his left hand, according to Tampa Bay Times coverage of the incident. Doctors determined the boy had 13 fractures, including his skull.The father, then 29, was arrested after Kody's great-grandmother told police she saw him shake the baby. She later recanted her statement, and no other witnesses testified that they saw James Duncan abuse his son.During the father's 1996 trial, prosecutors told the jury that James Duncan shook his son and yanked on him so hard that he broke his baby's bones. They also revealed in court that he was once a suspect in a 1991 shaken baby investigation of a child he was babysitting, but was never charged.It took that jury an hour to convict the father of 13 counts of aggravated child abuse.James Duncan had no prior criminal convictions. Still, Pinellas-Pasco Circuit Judge Timothy Peters gave him the maximum sentence: 70 years in prison."If the courts of this state and the laws of this state are not here to protect the babies, of all people," the judge said at the 1996 sentencing hearing, "then I don't know why we are here."This latest appeal was filed in December 2015 and it was based on a peer-reviewed medical article published the year before. The article chronicled the results of a study that concluded there is a "high likelihood" many babies with broken bones were not victims of child abuse, but were suffering from a "bone fragility disorder" or a vitamin D deficiency.Dr. Marvin Miller, a medical director at Dayton Children's Hospital in Ohio, authored the study. The defense motion said he examined the infant's medical records and X-rays. The doctor noted that there were no signs of bruising, which often indicates abuse."It is my professional opinion that the cause of injuries . . . was a result of metabolic bone disease and not child abuse," Miller's report said.The study, James Duncan's motion stated, disproved the state's contention that he struck his child. Kody Duncan, who could not be reached for comment Friday, eventually recovered from his injuries. The father's attorney, Lisabeth Fryer, also could not be reached for comment Friday.The Pinellas-Pasco State Attorney's Office argued that the defense's appeal should be denied because the window for an appeal based on new evidence had expired. Pinellas-Pasco Circuit Judge Michael Andrews sided with the state at the circuit level. But the 2nd District Court of Appeal disagreed.James Duncan is now 50 and being held at Avon Park Correctional Institution in Highlands County. His two sons' names and a heart are tattooed on his right arm, according to prison records."We can't get back all those years we lost," Kody Duncan wrote to the court. "But we can start new memories and develop and even stronger relationship when he gets out."Times senior news researcher Caryn Baird contributed to this report. Contact Laura C. Morel at [email protected] Follow @lauracmorel.