A Samsung tablet left by a fighter for the Wagner group exposes its key role - as well as traceable fighter codenames.
And the BBC has a "shopping list" for state-of-the-art military equipment which expert witnesses say could only have come from Russian army supplies.
Russia denies any links to Wagner.
The group was first identified in 2014 when it was backing pro-Russian separatists in the conflict in eastern Ukraine. Since then, it has been involved in regions including Syria, Mozambique, Sudan, and the Central African Republic.
Wagner's fighters appeared in Libya in April 2019 when they joined the forces of a rebel general, Khalifa Haftar, after he launched an attack on the UN-backed government in the capital, Tripoli. The conflict ended in a ceasefire in October 2020.
The group is notoriously secretive, but the BBC has managed to gain rare access to two former fighters. They revealed what type of person was joining Wagner - and its lack of any code of conduct.
There is little doubt that they kill prisoners - something one ex-fighter freely admits. "No-one wants an extra mouth to feed."
This supports other parts of the TV documentary - Haftar's Russian Mercenaries: Inside the Wagner Group - by BBC News Arabic and BBC News Russian. Its other revelations include evidence of suspected war crimes, including the intentional killing of civilians.
Its contents include maps in Russian of the frontline, giving confirmation of Wagner's significant presence and an unprecedented insight into the group's operations.
A military analyst told the BBC that some of the weapons technology would only be available from the Russian military. Another expert, a specialist on the Wagner group, said the list pointed to the involvement of Dmitry Utkin.
He is the ex-Russian military intelligence man believed to have founded Wagner and given it its name (his own former call-sign). The BBC tried to contact Dmitry Utkin but has received no reply.
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