'Little Miss Innocent' dives into Kaitlyn Conley's conviction in poisoning death of ex-boyfriend's mother

In 2017, Kaitlyn Conley was found guilty of manslaughter in the poisoning death of her ex-boyfriend's mother Mary Yoder. Seven years later, the 31-year-old continues to maintain her innocence and wants to keep appealing her conviction.

ABC News Studios' chilling three-part docuseries "Little Miss Innocent: Passion. Poison. Prison." launches on Hulu on Sept. 20 and features new interviews with the Yoder and Conley families, investigators and attorneys involved in Conley's trial. It also includes an exclusive interview with the incarcerated Conley.

Conley, from Sauquoit, New York, went on trial twice for second-degree murder following the July 2015 poisoning death of Whitesboro chiropractor Mary Yoder -- who was her employer in addition to being her ex-boyfriend's mother. The first trial resulted in a hung jury, but she was found guilty of first-degree manslaughter in the second trial and sentenced to 23 years in prison.

After her conviction, Conley and her attorneys filed multiple appeals and continue to maintain her innocence. Her attorney is currently preparing a motion to the Appellate Division.

"I miss Mary, and I really hate that this situation has kind of colored my relationship with her," Conley said. " 'Cause I feel like I can't really miss her because I'm fighting for my own life."

After Conley was convicted, some of Mary Yoder’s sisters supported her and launched a campaign to try and prove her innocence.

Conley presented herself as someone who could never have committed the crime with her appearance, charm and seemingly innocent demeanor. She was seen by some in the community as a young, attractive woman standing trial for a murder that she may or may not have committed.

Conley tries to place blame on 2 people who she says knew more about Mary Yoder's death

Conley was introduced to Mary Yoder through her son Adam, with whom Conley was in a relationship. The pair met at a high school graduation party.

"Obviously, I liked him, thought he was quirky and was fun, and it wasn’t bad at the beginning," Conley said.

According to both Conley and Adam’s friends, the two appeared to be in love. Adam even got Conley a job as an office manager -- the same position he held -- at his family's Chiropractic Family Care business.

"The first year, my relationship with Adam was pretty good," Conley said. "Then there was a noticeable shift in him, and I didn't quite understand it."

Adam would also sometimes black out from drinking during this time, Conley claimed -- an allegation that was discussed during her trial.

Some friends and family described their relationship as toxic, indicating that they both had troubling behaviors.

"He was just as toxic as Katie, as far as not being a healthy relationship," Adam's sister Tamaryn Yoder said.

Adam and Conley had a tumultuous on and off again relationship. Conley even accused Adam of sexually assaulting her during the relationship.

There is no evidence to support Conley’s allegations that Adam sexually assaulted or harassed her, police said. Adam also denies the criminal allegations made against him.

Feelings between the two worsened when Conley, Adam and Bill Yoder (Adam's father and Mary Yoder's husband) became suspects in Mary's death.

Conley claimed both Adam and Bill knew more about Mary's death than she does.

Police found colchicine under Adam’s car seat after the Oneida County Sheriff’s Office was tipped off by an anonymous letter that Conley would later admit to writing.

How did Kaitlyn Conley become a prime suspect?

During the initial stages of the police investigation, Bill and Adam were under scrutiny. Bill came under suspicion because he began dating Mary's sister following her death.

Adam was suspected after an anonymous letter to the police pointed out that he had a bottle of colchicine in his jeep, which turned out to be true.

The case took a significant turn once the police interviewed Conley. They asked if she could come in to answer some questions.

"Katie seemed, I don’t know if I would say shy, but just very meek, mild, um, she worked in the office, she knew the family, she had a relationship with Adam," investigator Robert Nelson said. "During the interview she keeps talking about how suspicious Adam was acting. You know, in my mind, all of a sudden, she’s pointing a finger at Adam similar to the letter."

Investigator Mark Van Namee asked Conley if she had written the anonymous letter to the police, and she admitted to doing so.

"We had always said, you know, the person that wrote this letter is definitely gotta be considered a suspect in our case," Van Namee said.

Police looked at Conley more closely after she admitted to writing the anonymous letter.

"As I’m talking to Katie, and she comes back with the response about, 'Yeah, they [men] don’t use poison, that’s a lady’s weapon,' with a smirk, that was, like, maybe the light bulb moment," Van Namee said. "We were convinced that, you know, we had the right person."

This convinced police that Conley was responsible for Mary's death, according to Van Namee.

Conley is currently at the Bedford Hills Correctional Facility in New York State. She hasn't admitted to killing Mary and said she'll continue to fight for her freedom.

"It just, it felt like everything failed," Conley said. "I put all my faith and all my trust in the system and these people, and it didn’t work. It felt like we’d been let down."

Conley's parents and sisters still believe she is innocent and support her while Mary's husband and children say they despise Conley. According to Adam's sister Tamaryn, he still blames himself for bringing Conley around his mother.

"I hope she never makes it out of prison," Tamaryn said. "I’d be OK if she made it to 22 years and then got killed in there. I’d be happy."

Conley said she has no plans to apologize or admit her guilt.

"The Yoders don’t need closure, and they don’t need that from me," Conley said. "They need help, and they need to figure a lot of things out, but that has nothing to do with me. It has nothing to do with me."