Probably from this:
Chloroquine is a potent inhibitor of SARS coronavirus infection and spread
That's a 2005 paper published by the NIH funded/directed by Dr. A. Fauci.
chloroquine has strong antiviral effects on SARS-CoV infection of primate cells. These inhibitory effects are observed when the cells are treated with the drug either before or after exposure to the virus, suggesting both prophylactic and therapeutic advantage.
In Africa, it's called the SundaySunday drug, because you should take your dose every Sunday to prevent Malaria... so safe for OTC in many nations, there was just no demand for it to be OTC here in the US.
The very existence of this means that the EUA that the FDA granted Pfizer was null and void (there cannot be an existing therapeutic). That's why the CDC, NIH, only tested on already hospitalized patients... that's when it's too late. But it wasn't too late for the FDA director to take a position on Pfizers board... where he earns 230K a year for just showing up....
Yeah, nothing unethical about any of that...