I have actually had a theory on MM’s phone for some time.
But in order for this theory to apply/ be possible, the killer(s) would have to have been hired to commit the murders - and hired by someone extremely close to MM.
Basically the theory is that the taking and discarding of MM’s phone was part of the plan and it had a specific purpose.
An app, such as Life 360, would show anyone in MM’s Life360 circle the location of her phone. There is no record created when someone checks the location of someone in their circle.
(For instance, in our family, our L360 apps are always running in the background. If I want to know where my husband is, I simply glance at his location. Neither my phone nor his phone will have any record of me checking his location. And of course, I’m not really seeing where my husband is, I’m seeing where his phone is.)
Upon leaving, MM’s phone may have been taken and used by the murderer(s) to communicate completion of the job to someone else through this sort of app. A message sent simply by the location change of MM’s phone, communicating “we’re gone”, and with no digital footprint.
Speculation/ theory
All my opinion only