Right. Joseph's phone pinged a tower in Fallbrook at 8:28. So that was either the last sign of life for JM, a pocket dial, or I theorize it might have been Merritt trying to access JM's phone and he accidentally called himself in doing so as Chase was the last person Joseph called.
IMO the fact that someone was creating fraudulent cheques at JM's house at 7.59 pm supports a cast iron inference that JM was dead or incapacitated by that time.
I think the fact that CM lied about 'ignoring" this call is a pretty big tell.