EndlessPlaid

Now one question I’d like to know the answer to is how they got routed over this storm, was this in the flight plan, did ATC send them this way? And did they request a deviation from the flight plan prior to this?

To be clear, this is a plausible scenario, there'll be an investigation by the NTSB who will explore all the possibilities and may find contributing factors beyond this first guess. I'm putting this out there because there are some conspiracy minded people saying bad things.

This Learjet crash sure looks like an icing situation. They were at 37,000 feet over a thunderstorm and suddenly started descending. There's a transcript of ATC calls that mentions the icing. Ice accumulation is faster on tightly curved surfaces. The tailplane is basically small wings, which means tighter curves, so ice accumulates on the elevator at the back. The ice makes it less effective, you have to apply greater control deflection to keep the nose up, and then you run out of control authority, or push it too far and stall the tail. The nose pitches down and you pick up speed, exceeding limits of the aircraft. The horizontal stabilizer may have been torn off during descent, it would have an IAS of over 400KIAS at this point. That's over the 340KIAS limit. Mach number would be about 0.88, and when you factor in turbulence the stress on the airframe is even worse. So, I expect the horizontal stabilizer didn't come off until the overspeed condition.