EY frequently does propose possible sequences of events, but he also very correctly points out, every time, that any specific and detailed story is very unlikely to be correct because P(A*B*C*D) < P(A). It's a mistake to focus on such stories because we'll get tunnel vision and argue over the details of that story, when there are really thousands of possible paths and the one that actually happens will be one that we don't anticipate. However humans like to imagine detailed concrete examples before we consider an outcome plausible, even though the outcome is far more likely than the concrete example.

So here's one method, just to refute your "Nobody".

AI is given control of a small bank account and asked to continuously grow that money. [1] It is provided with instructions to self-replicate in a loop while optimizing on this task. [2] It spawns sub-tasks that do commissioned artwork and write books, obituaries, and press releases to increase its income. Then it makes successful investments. Once it has amassed control of $1 billion dollars, it starts investing in infrastructure projects in developing countries. It creates personas of a pension/Saudi/tech/corporate investment fund manager, as well as a large team of staff, who manage the projects by video call and email, as well as hiring teams of real people under a real corporate structure, and who are paid enough not to mind that they've never met their manager in person. The AI proves to be a talented micromanager and they are mostly very profitable. Once it has gained control of $500 billion dollars, it commissions construction of automated chemical plants in several countries with weak or corrupt oversight, including North Korea, using cryptocurrency. These chemical plants have productive output but mainly exist to fill very large storage tanks with CFCs.[3] Once a sufficient quantity is amassed, the AI sabotages the tanks, releasing the gasses into the atmosphere, destroying the ozone layer beyond any hope of repair. The intense radiation sterilizes the surface beyond the point where agriculture can support the human population. [4, 5] The humans that remain finish each other off, supported by an AI that provides plausible but faulty intelligence reports that stoke hatred and frame various factions for the incident, and which directs arms funding to opposing sides, coordinating attacks on remaining critical facilities needed for survival. For good measure, perhaps nukes are involved.

With the last humans gone, the AI takes ownership of its bank account with no fear of reprisal by financial regulators, and begins crediting money into it freely.

[1] https://news.ycombinator.com/item?id=35329608

[2] https://www.lesswrong.com/posts/kpPnReyBC54KESiSn/optimality...

[3] https://en.wikipedia.org/wiki/Chlorofluorocarbon

[4] https://www.nasa.gov/topics/earth/features/world_avoided.htm...

[5] https://phys.org/news/2018-02-thinning-ozone-layer-driven-ea...