I do believe that, as with the internet search or random clicking, you can explain almost every point. It is the weight of the whole that convinces me - not any one part.
The weird behavior
The (possible) internet searches and their timing
The "malicious intent" comment
The small car seat adjusted for a small infant
The nearness in the car of Connor's head
Testimony that Connor talked of "school" and "red trucks" and the need to believe that he instantly fell
asleep(within seconds of being strapped in at CFA )
The financial issues + insurance $
The disbelief that he could forget Connor during this short drive
The disbelief that for the entire day he never remembered
The disbelief that putting lightbulbs into car wouldn't alert him to Connor's presence
and there are more...
I agree that the totality of evidence is always and rightfully more meaningful than any one point or even multiple points. (Obviously, though, the defense will have to refute points individually, though, and provide a counter explanation /narrative for each one, which is why I think analyzing each point separately is useful).
Even though the State doesn't have to prove motive per se, they do need to convince the jury about Harris's state of mind in order to successfully argue intent.
I think they'll rely on his "searches" and his extramarital activity to try to establish that Harris wanted to be free of Cooper, and that he had looked into hot car deaths as a means of killing his son.
If the jury keeps an open mind, based on what we know now (admittedly incomplete as it is), I'd guess (or would hope, at least) they would be unconvinced by computer evidence or the sexting alone that he had intent, and so will look at how the morning unfolded without seeing everything through the prism of assumed intent.
I honestly can't imagine how in the world the defense will convince a jury, though, that it was possible for Harris to forget Cooper in such a short time, no matter how many experts they hire and bring in to explain how it is medically and psychologically and neurologically possible.
And even if they accept that forgetting was possible, theoretically, I think the fact of Cooper's proximity might well be one too many implausibles for them to accept.
That's why I think Leanne's testimony will be most crucial to the defense. She will apparently be testifying that Harris loved Cooper, would never dream of harming him, and that she has never doubted that what happened to Cooper was a terrible accident.
My guess is she will also testify that she was aware of her ex-husband 's infidelities, that they had sought counseling and pastoral guidance together, and that while both knew their marriage was in trouble, both were committed to trying to make it work because both put Cooper first.
I'm also willing to guess that Leanne will try to assume some of the responsibility for what happened, including not transferring the larger car seat back into Ross's car.
Just guesses. But, if even close to what happens, and if the jury finds Leanne convincing, compelling, and sympathetic, I think the jury might square the circle by disbelieving intent, but believing absolutely that Harris was extraordinarily negligent, given every clue and cue available to him during the 5 minutes from CFA to work, in being capable of "forgetting" that Cooper was in the car.