Because Marta was one of the investors in the film does not in any way make the film suspect. Fabian Marta was one of thousands of investors who made the film possible. Among thousands of any group of humans, you're bound to find a bad apple or two.
So shame on those who scoured among those thousands of investors to find one they could exploit to try to damage or compromise and/or falsely implicate a film exposing a topic the leftists don't want to even acknowledge or talk about, much less be featured in a popular movie. Such tactics are immoral, dishonest, reprehensible, and evil.