In real life, there were no secret tunnels found under 657 Boulevard.

Real-world investigators did find female DNA on one envelope, but it did not lead to an arrest or a breakthrough in the case. Deep Dive Resources

'The Watcher' Season One, Episode 5 Recap: 'Occam's Razor”

Ellie discovers a Facebook group for former students of an English teacher named Roger Kaplan , who used to have his students write "love letters" to houses. This makes Roger a primary suspect for the origins of the Watcher's poetic and creepy writing style. Fact vs. Fiction

While the series is famously based on a true story, this episode introduces several highly fictionalized elements:

Nora becomes convinced that Dean is the one writing the letters to scare the family into selling the house, especially after discovering his financial struggles and a mysterious video of a girl with pigtails in their bedroom.