Ok, just some thoughts... SPECULATION
ICE involvement: while I believe they are likely just being used for the expertise in computers, evidence gathering and an extra resource to do with surveillance, (all the cool federally funded spy gadgets), they could be involved because it has been RUMORED that JF wasn't too choosy about his employees, (trying to save money and such). Could he have either recently or in the past have hired an illegal immigrant that ICE might have helped in questioning? Maybe not a prime suspect, but someone who LE would likely want to at least question?
Cell phone activity: This is interesting information we are learning - especially the idea that the phone was already turned off before the 5:42 final communication with the cell network. Why would the phone be turned back on for that final ping, (or whatever it was?)?
Trying to make sense of this, let's try a couple of scenarios:
Scenario ONE: First let's go with MC being the one that turned her phone back on. This seems to work, (MC attempts call for help), although we need to account for her the entire time the phone was off, (or at least why she wasn't receiving texts and calls were going to voice-mail). Would she have done that by choice? It doesn't sound like she ever turned her phone off. IMO that means someone would have forced her to turn phone off, (or asked her convincingly), and when she decided things were turning bad she attempted to turn it on and make a call for help? Plausibility is still sort of low on this one, IMO. If she's not the type to turn her cell phone off, maybe she left or was taken outside cell service area and that explains reason for messages not going through, (in this case, the phone wouldn't be "turned back on" it would just re-enter cell service area at 5:42 pm - which takes us to our next scenario).
Scenario TWO: Suspect(s) are in control of phone. I would imagine, after the crime is committed the first thing a suspect would do to a cell phone would be to remove the battery -- someone said they had this exact same phone, to that person I would like to know what does removing the battery from MC's phone require? Is it simple for someone unfamiliar with the phone? If the phone is slide open, (or flipped or whatever), does it turn itself back on automatically? Is that position required to remove battery?
Other than removing the battery, a suspect may think of stomping on it or attempting to crush it in some way. What if stomping on it turned it on for a split second, just long enough to register on the cell network? Sounds iffy to me and IMO causes me to lean towards the idea that the phone, (and maybe MC?) were taken outside of service coverage area, (possibly MC going willingly - but likely not). Then, when the suspect drove back into the service area all those text messages and voice mails would have caused the phone to immediately buzz, alerting the suspect, who would then immediately removed the battery/destroy the phone. Maybe he even had to dig it out of a pocket as the body was being transferred from unknown location to CB location?
The car wash (RUMOR): The person who noticed the water streaks on the rear of MC's car coming from under the rear spoiler - good job. This does lend some to the car wash rumor, IMO. Maybe it only poured out because of the steep incline the vehicle was put in to flatbed or tow it? Do you also have a guess as to how long water tends to stay trapped under those rear spoilers? Could it be days?
Also, if she did have a passenger, maybe that passenger offered to pay for the car wash, and that is the only reason she did it? She may not have been stressed out/under duress while at the car wash as much as confused because it was something unfamiliar for her to do. Sort of like pumping gas at a different station than the one you always go to - easy to get confused, i.e. "Do I select wash type before or after inserting coins? Oh, there's an attendant, I'll let him do it?"
