This week Volkswagen has taken a significant (but far from final) step in drawing a line under the Dieselgate scandal, accepting a $4.3 billion fine, agreeing to plead guilty to criminal charges and accepting six executives must face federal charges.

But along with this plea bargain has come a number of lurid admissions that lay bare at least some of the depths VW employees sunk to in order to create and then try to hide the now infamous cheat software behind its emissions defeat devices.

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The full depth of analysis of VW’s signed agreement is best credited to the BBC’s Theo Leggett, whose full work you can read here. In brief, it highlights how:

- the plan to cheat emissions legislation was born in 2006, when VW supervisors realised they couldn’t meet targets for an engine set to be launched in 2007.

- the cheat device was then based on a system developed by VW's subsidiary Audi, but which engineers stressed should "absolutely not be used" in the US.

- immediately, engineers on the project "raised objections to the propriety of the defeat device".

- a manager responded by insisting it was used and "instructed those in attendance, in sum and substance, not to get caught".

- in 2007 engineers objected again - and were over-ruled again.

- the cheat software was then refined and improved over time, and came to be used as standard.

- a spate of breakdowns caused by the cheat software was actually fixed, and let to more exhortations from senior management to keep the software concealed.

- engineers and management were told to destroy documents referring to the software.

- when, in 2014, the California Air Resources Board highlighted the issue, VW supervisors "determined not to disclose to US regulators that the tested vehicle models operated with a defeat device". Instead they "decided to pursue a strategy of concealing the defeat device… while appearing to cooperate".

- a single employee acting "in direct contravention of instructions from supervisors at VW" finally confirmed the cheat codes were used.

- even then, engineers were told to "check their documents”. Thousands of documents were subsequently deleted.