December 12, 2016 05:00 PM

More than 20 years after she  was convicted of murdering Adrianne Jones, Diane Zamora tears up thinking about her teenage victim.

“It wasn’t her fault, but she wouldn’t have been in that position had I not lost my temper,” Zamora tells People Magazine Investigates from behind bars. Monday night’s episode of the Investigation Discovery series will focus on the case.

Zamora still maintains her innocence in Adrianne’s December 1995 slaying, which stunned their Texas community and made national news. But Zamora doesn’t deny her complicity: She admits that she witnessed her fiancé, David Graham, kill the 16-year-old, and then helped hide it. But she insists she never killed anyone or set out to do so.

(Graham has struck a similarly remorseful tone in past interviews, telling the Dallas Morning News in 2008 that Zamora was the “motivator.”)

“I think I remember seeing [Adrianne] one time, just noticing her,” Zamora says on PMI‘s upcoming episode. “I have a vague recollection, but I’d never heard her name, anything about her. I’d never seen a picture. … I didn’t know anything of her at all.”

But authorities say what Zamora learned about Adrianne from Graham was enough to send her into a murderous rage: According to a confession Graham later gave police, Zamora became inconsolable shortly before the murder when she learned Graham had had sex with Adrianne.

• Watch our new true crime show, People Magazine Investigates, which continues with an episode on Adrianne Jones’ murder on Monday at 10 p.m. ET on Investigation Discovery.

“The only thing that could satisfy her womanly vengeance was the life of the one that had, for an instant, taken her place,” Graham said.

In her own statement, Zamora reportedly told Graham “that the ‘purity’ of their love could only be restored by killing Adrianne,” one law enforcement source told PEOPLE at the time.

Now — decades after the killing and with years before either Graham or Zamora is eligible for parole following their murder convictions — Zamora is opening up about what she says happened to the exuberant and well-liked Adrianne.

“I think I deserved something,” she says, “because I don’t just sit here and say, ‘Oh, I bear no responsibility.’ ”

People Magazine Investigates airs Monday (10 p.m. ET) on Investigation Discovery.

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