NoCourtesyMost car have a tracker integrated. Call the car company, see if they can locate it. Think by deduction;
-he most likely didn't commit suicide or any form of self-harm, as you mentionned #14, he seemed fine in the morning when he left your home. Moreover, he seems to have a full family and a loving and caring son, no dad would ever forget that
-he didn't check-in work, so whatever happened, it had to happen between 9h30 and the time it takes him to get to work. This might help you narrow down essential details for the police
-the notes he left means whatever he did was most likely premeditated. Did he say anything that seemed odd in the notes? Maybe a word or expression he doesnt say much, maybe a reference to an event from the past? What is the tone of the notes? Does he seem determined? Sad? Helpless? Mad?
-you may be able to track him through his car, gps, or phone, even if it is off
-do you own any weapons at home? I am not from the US so dont know the gun reglementation in Pensilvania. If yes, are they still there? If not a gun, did ammunition disappear?
-try to think of when he went to work, did he do something he usually doesn't? Did he forget something minor that he usually brings to work? (My dad for example always brings floss...) That could indicate you whether he was planning on getting to work or not, but then again, why would he have left notes that morning if that was the case?
We are all with you, stay strong
Well, in the note to his parents, his note was more accusatory and angry then sad and apologetic, the police are aware of this as well, but as I said, they live all the way in Tennessee and he doesn't have the funds to drive that distance. Also, even if suicide isn't where he was going, he talked in the notes as if he was leaving at all. The note to me said; "Be strong for Beth (my mom) and your brothers, the next weeks will be hard on them."
As far as weapons go, his phone case is like a utility case, and it has a bunch of sharp objects in it, including a nice.