Taking things out of order here:

We engineers are not so dense as is supposed.

I don't think engineers are dense! I suggested earlier in this thread that "achievement in the environment" is the proper subject of study for philosophy. Who excels at achievement in the environment better than engineers? You don't know it, but quite a bit of your discussion about how engineers work, succeed, fail, and recover has become part of the foundation of my personal philosophy.

It's amusing you bring up structural engineering,

It may be amusing, but I know who I am talking to. I have a good idea of the subjects that interest you and expected you to write something that would serve as common ground for both of our views.

True, but the structural redundancy, however it is said to exist, is a property of the structure itself and not something that can be attributed to the structure by the arguments of others in a way that causes the property to change if the nature of the attribution changes.

Agreed. This is the common ground I was looking/desiring/motivating/intending/jonesing for. I am confident that I could round up from various philosophy forums plenty of people who would argue that because it is hard to point to structural redundancy in a building, that it exists, then, only as a subjective abstraction in the engineer's head. I'll pause while you entertain yourself with ways you could demonstrate the objectivity of structural redundancy to them...

Consider an engineer who goes on site to assess a building's redundancy. From the moment he studies the first structural members, he knows about the building's redundancy. He just doesn't know everything about it at first, and will never know everything about it. Because his knowledge is finite, we do not say that he is does not study the redundancy, or that he studies it indirectly, or that redundancy exists only in his head.

I said above that I knew you were interested in structural redundancy and predicted you would expand on what I had written. Yet, all I have seen from you over the years are words on my computer screen. I am proposing that the words you have fed out to us constitute the first fibers of your motives. If I am wrong about your motives or interests, it not because I have not seen them, but because I have not seen enough of them and/or I am not skilled enough in predicting behavior from a limited set of writings. And if you tell me what your true motives are, you are just feeding me more words.

Notice how this differs from the view where there are actions on the surface and "motives" underneath driving them. Motives are "attributed" only in the sense that we treat complex patterns of action is if there were a singular driving (or attracting) force behind them. (The point here is not necessarily to deny that such singular forces exist, but to suggest that they are not what we speak to when we speak of motives.)

An individual's motive is a thought. It exists inasmuch as a thought can be said to exist.

I suggest that you want to learn about the pawn by cutting it open.
Let's say a guy watches only Catherine Zeta-Jones movies. Sure he has thoughts about her, but to limit his motive to just his thoughts leaves Zeta-Jones out of the equation.

A group's motive exists according to a different and more problematic way of thinking. We're not considering an individual's motive.

The actions taken to delay the video to bait conspiracy theorists will likely be different than the actions taken to delay it so as not to influence any trial. (Although, I suppose they could delay the video for legal reasons knowing full well that conspiracy theorists will make fools of themselves anyway.) It is the actions that are considered sinister--not just the private thoughts and feelings of the individuals as they carried out those actions.

But in the infrequent case where that husband's motives do demand first-class attention aside from his actions, how shall we reason about them?

Motives are an aspect of the actions and the contexts they occur in, just like redundancy is an aspect of the building and how it responds or would respond to various environmental stresses. One way we reason about motives to apply our experience of observing how actions played out in other cases.

And if the argument is written such that motives are argued first, and then upon that conclusion is based an assertion that action was taken, how shall that supplant evidence of the action?

The husband enjoys his wife's company when she is laughing. That is not enough to conclude that he has told her a joke.

But carrying it further, is the motive truly right in front of us? Doesn't this amount to attributing a motive of retribution to Johnny?

How about we use the term "classify" in this case? We classify the pattern of action and reaction here as "retribution" or "having the motive of retribution." We might be wrong, of course, because our knowledge and skill is limited. It would be like picking up an object thinking it is a pen, and upon clicking it, discovering it is really a mechanical pencil. You acquired one more piece of information that allowed you to overcome the ambiguity.

Now consider a homeowner who takes his landscaper to small claims court because the landscaper did not live up to their agreement. We say the homeowner also has the motive of retribution. But is there something common between Johnny and the homeowner? If there is, it is in the patterns of actions and reactions that take place.

A more interesting example would be if Bobby hits Johnny, but Johnny hugs Bobby back instead. Here an intent-based model can go many directions. We lack a singular, universal human rule by which to interpret Johnny's behavior confidently.

That's true. We haven't seen enough yet, either from Bobby and Johnny or from our experience in life to judge the action.

If Johnny were compelled to reveal truthfully his motive, we might hear such things as, "He is my brother; I take his abuse with familial patience," or "Bobby is autistic; he doesn't know he's not supposed to do that," or "Jesus said to love your enemies; and I want to be like Jesus."

Johnny's speech is additional action. It is not so much that Johnny "revealed" his motive, as it is we finally observed enough. What Johnny says does have to fit in with his prior and consequent actions. (There was one kid in high school, a real stoner, who came up to me one day and told me he loved Jesus and that I should follow Jesus too. I thought he was just teasing me. It was only later after observing him long enough that I realized he was dead-serious and that he really did become a born-again Christian.)

As you're aware, conspiracism relies greatly on an "appeal to motive" -- the notion that if someone had a motive to do something, he naturally did it whether the results are visible or whether it was even possible to do.

Yes, and your points are well-taken. We, too, introduce motive often, such as when we suggest Bart Sibrel is in it to sell videos, or Jack White does it to pump up his ego, etc. But of course, we verify that Sibrel sells videos and we observe the repeated pattern of him pushing his videos before we make the charge.