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WILLMAR, Minn. — For the past several months, ABC News has been working on a special two-hour "20/20" focused on the story of Jacob Wetterling . Set to air at 8 p.m. Friday, Oct. 13, the show will include interviews with those closest to the case — including Patty and Jerry Wetterling, Jacob's parents.

Patty Wetterling announced the special on , co-written with Joy Baker, titled "Dear Jacob: A Mother's Journey of Hope." The book will be released Tuesday, Oct. 17.

According to the announcement, crews from have visited Minnesota several times since April, interviewing investigators, suspects, witnesses, reporters and many others close to the case, including Baker, a freelance writer from New London.

A story about the book — and the journey both Wetterling and Baker took to write it — will be published on Saturday, Oct. 14, in the West Central Tribune .

Jacob Wetterling was abducted on Oct. 22, 1989, near his home in St. Joseph . The kidnapping set off a nationwide search and, for 27 years, his family worked tirelessly to find and bring Jacob home. Patty Wetterling became a nationally known advocate for missing and exploited children.

It wasn't until the fall of 2015 that investigators were finally able to make an arrest in the case. Denny Heinrich was arrested on child pornography charges after law enforcement searched his home for evidence connected to both the Wetterling case and a separate kidnapping and sexual assault case.

In a plea deal with authorities, which was agreed to by the Wetterlings, in early September 2016, Heinrich confessed to the Oct. 22, 1989, kidnapping, sexual assault and murder of Jacob. He led investigators to where he had buried the young boy's remains in a field near Paynesville . Heinrich also confessed to the January 1989 abduction and sexual assault of Jared Scheierl.

As part of the plea deal, Heinrich was convicted of one count of receiving child pornography and was not criminally charged with any of the crimes against Jacob Wetterling or Scheierl.