Learn French: Le procureur veut contredire cette version. - The prosecutor wants to contradict this version.

Actually, no! While dire and redire use the -tes ending (vous dites, vous redites), most other verbs ending in -dire take the regular -ez ending. So, you would say vous contredisez.

Is a procureur the same thing as an avocat?

Not exactly. An avocat is the general term for a lawyer or attorney, such as a defense attorney. A procureur is specifically the public prosecutor or district attorney who brings criminal charges against someone on behalf of the state.

In this legal context, what does cette version usually refer to?

In French police and legal contexts, une version is common shorthand for une version des faits (a version of the facts). It refers to a suspect's or witness's specific account of what happened, or their side of the story.

How would I apply this lesson's grammar to say "Supposing that the prosecutor wants to contradict this version..."?