On August 9, 2018, a few days prior to the murders in Frederick, and a week prior to Watts interrogation and confession, Vanessa Bennett, the victim of a family murder in Aurora in 1984, broke her silence.
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From 9News.com:

Vanessa Bennett sat under a picnic shelter on a muggy Arizona morning and talked for the first time about the physical and emotional toll she bears as the only surviving victim of one of Colorado’s most brutal crimes.
Bennett is 38 now, and the scars of the 1984 hammer attack that left her clinging to life are visible. Vanessa’s life changed on Jan. 16, 1984. Her grandmother, Constance Bennett, went to the family’s home that morning after her son and daughter-in-law didn’t show up for work at the family’s furniture business. She walked into a scene of absolute horror: Bruce Bennett crumpled near the bottom of the stairs, Debra Bennett and Melissa dead in their bedrooms, Vanessa barely breathing.
“I was in a coma,” Vanessa Bennett said Thursday. “My jaw was wired shut. I had tubes in my nose to eat. I went through physical therapy. I had braces on my legs.” The physical injuries were difficult to overcome.
“I had paralysis on my left-hand side,” she said. “So, like, I felt handicapped, you know. I had a lot of anger issues growing up. My family really couldn’t handle me – I just wore everybody out with my problems.”
Some of those problems were fueled by the things other kids said to her. “I was made fun of in school because my parents were killed,” she said. “I was made fun of because the hammer man or whatever you want to call it was going to come to my house and hurt everybody when I had slumber parties and stuff. I was made fun of for a long time.”
She was frank as she discussed her life. She has been diagnosed with bipolar disorder, post-traumatic stress disorder, and attention-deficit hyperactivity disorder. She also struggled for a decade with substance abuse problems and got into multiple scrapes with the law.

During her interrogation of Watts, Agent Lee cited Bennett’s “survivor’s guilt”, saying:

She said I wish I could’ve died with them.

At this point Lee was fielding a scenario where one of the children died by accident [say, Ceecee from an extreme allergic reaction], and Shan’ann freaked out and then killed the other child and perhaps herself.
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The second scenario Lee cited was the Castle Rock case, where a mother was found guilty of smothering her two children to death.
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Denver Post [November 27, 2012]:
Prosecutors said Kelli Murphy smothered and killed her two young children in May 2011 because she was not going to share custody of them with anyone else.
On Tuesday, a jury agreed.
“This is a woman bent on control,” prosecutor Chris Gallo said during closing arguments. “Controlling her kids, her husband and her divorce … It was Kelli’s way or no way.” Douglas County District Judge Vincent White immediately sentenced her to two terms of life without parole after the nine men and three women on the jury found her guilty of two counts of first-degree murder after deliberation and two counts of first-degree murder of a victim under 12 years old.
When her sentence was read, Murphy, 43, remained silent and looked forward until she was led from the courtroom. Throughout the case, prosecutors claimed that Murphy killed her 6-year-old daughter, Madigan, and 9-year-old son, Liam, when she became distraught over her impending divorce from her husband, Robert Eric Murphy.
Gallo said Murphy was a controlling, angry, calculating woman who did not want to share the children with her ex-husband.
“I want 100 percent custody of the kids and 100 percent of your salary,” Gallo told the jury that Kelli Murphy had told Robert Murphy. “I’m going to make your life hell.”