If a single engineer developed the engine, including the software, it would be quite likely that he or she came up and implemented the cheating solution alone.

If a single engineer developed the engine, including the software, it would be quite likely that he or she came up and implemented the cheating solution alone. But that's not how things work. Imagine being in the team that develops an engine. Some prototypes are built, measurements are done, way too high emissions are noted. Who gets the results from the measurements? The project lead, of course. Then the lead calls in folks from different parts of the team (or even different teams involved), and they brainstorm what to do. This becomes a big topic, because it puts the whole project at a risk. If at some point the problematic values simply disappear, any diligent project lead has to investigate where the improvement comes from, if only to make sure there's no regression. How would the scenario look like so that the project lead never even noticed? The environmental testing reports directly to a software developer (but why would they?), who implements the cheating part. Without first asking the rest of the team if there are legit ways to accomplish lower emissions. All documents regarding the first test runs vanish (but why would they? it's not the tester's job to make sure the emission standards are being met), and the problematic emissions never become a topic. Somehow that sounds not realistic at all. So, I'm pretty sure the project lead knew about it. the project lead might have been an engineer by training, but his role was that of a manager.