I have wondered why the son knew they were missing too. But I think I understand how it might have happened.
If MC was going to an early meeting and then taking TC to work, wouldn't he be expected to come back home for awhile, until it was time to go pick her up? Maybe the son had been expecting him home all day, and got no response from either of the phones, and then found out she never went to work at all. I would call them in missing too at that point. JMO
I agree, the details that day don't need to be complicated.
It probably happened something like this:
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The son tries to text or call his dad, gets no reply.
The son calls Tina's work to ask her where he is, finds out she never made it to work.
The son continues to text and call, knowing now that Tina never made it to work---no replies.
Son calls Tina's boss again----finds out she never appeared the entire day.
As the day passes, the son grows
increasingly alarmed.
Calls 911 just prior to dark and reports them as missing.
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Seems pretty simple and logical to me. I don't know that a lot of people in this forum wouldn't follow that exact protocol in a similar circumstance.
At that particular point in time, the son most likely thought they had been involved in a car wreck or traffic accident . He was smart enough to have the vin# handy when he called 911, because at an accident scene, the first information written down is the license plate number and the vin# of the cars involved.
I don't see anything sinister or odd in the way the son behaved that day either.