"the CIA's Office of the Inspector General which ultimately concluded the allegations were unsupported."
"Webb's series led to three federal investigations, all of which concluded there was no evidence of conspiracy by the CIA or its employees to bring drugs into the United States.
.. sounds to me like it was investigated and nothing turned up?
If one was to read this very carefully, they're not saying it didn't happen, they're just saying the evidence to support the allegations no longer exists. For a top secret program, that sounds about right.
"the CIA's Office of the Inspector General which ultimately concluded the allegations were unsupported."
"Webb's series led to three federal investigations, all of which concluded there was no evidence of conspiracy by the CIA or its employees to bring drugs into the United States.
.. sounds to me like it was investigated and nothing turned up?