We're forced to believe some version of this, but I'll tell you that this version isn't just a little off, its way off. Who made up this version, anyway?
Perp could've 'slipped in' while the R's were at the W's.
Perp coud've attempted to move JBR using blanket, tape, wrist cord to a car, and she refused or fought back or screamed. OR perp could've decided JBR wasn't as expected, OR perp could've felt comfortable in the basement to assault and kill right there.
RN could've been written in the afternoon, and placed on the stairs as a tripwire in case a family member came down during the night. A loner perp would need a warning of a family member coming down to look for JBR missing from her bed.
Three page handwritten letter should be a clue that it wasn't written by a household member, neighbor, relative, coworker, etc., etc.