Someone brought up a good point the other day about what could have changed to let LE know where to look in the spring. My understanding is when LE gets a search warrant to pull cell phone records that it sometimes takes a lot of time to get all the detailed records that would include the Cell Tower pings or GPS locations of the cell phone.
And once they get the detailed records then I think it takes a lot of time for LE to sit down and do the mapping they would need to do to try to make sense of the records. They have to plot out all the pings, the cell phone tower locations, the times and dates of the pings, etc.
I think all of that takes quite a bit of time and so I could really see where LE may not have gathered all this research until after the cold had set in.
I have high hopes that LE has spotted something on the cell tower/GPS charts that show they stopped at a certain place for 30 minutes or more which is a rural place.
OT
On my phone, a couple years ago after I had learned how the cell tower/GPS signal works on the phone and how that information can be used by others ("the man" - LOL), my paranoia made me turn off the setting to where my location was not transmitted back to the phone company. I then quickly realized that if I ever got in a car wreck or was lost somewhere then nobody would ever find me so I turned back on the feature.