It's definitely possible that only a small group of engineers at +Volkswagen USA? knew the details of the big cheat, but they definitely can't take all the blame

It Could Be That Only A Few VW Engineers Really Knew About Emissions Cheating
Many are skeptical of VW’s claim that only a handful of lower-level employees are to blame for the doctoring of its vehicles’ performance for emissions testing, but In a narrow sense, it actually is possible. A surprisingly small number of people at any automaker are involved in writing the engine control software at the heart of the scandal.