There are a couple of things bothering me about the car being seen.
First, if the killer was driving Tom's car, wouldn't that person know his family would or should be out looking for him? Isn't that taking a very large risk of being spotted by family or friends....as small as Canadian is? What would be their plan if they ran across Tom's family looking for him. Why take that risk of being spotted?
Second, if Tom was driving that car, why did he not return home when expected? Where had he been driving? What was he thinking? Was he out driving trying to decide what he wanted to do? If Tom was driving through town all night, something was not right with Tom. This part of the suicide scenario would fit in perfectly. Trying to talk himself into or out of suicide? Possibly, but the last part of the scenario does not make sense.
What does make sense is the person responsible for Tom's final resting place, be it murder or suicide, was the one who parked the car and planted the phone.
BTW-have Tom's keys to his car ever been located? I cannot remember. All JMO of course!