I recently saw the film Kill the Messenger. The movie tells the story of Gary Webb, a journalist who wrote a story in 1996 that alleged that the CIA, in addition to funding the Nicaraguan Contras by indirectly selling arms to Iran, looked the other way while the Contras sold cocaine in LA and alleged that this helped start the crack epidemic of the 1980s.

Basically, I want to ask how substantiated this idea is by modern historians. I am not interested in Gary Webb and his credibility as a journalist or his story, just the historical facts of this claim in the 1980s. I know that the 1990s are currently not allowed for questions, but I hope it's alright as it is about events that transpired in the 1980s.

EDIT: And please, source whatever response you can find. And selling cocaine in the USA.