The FBI elite agent who investigated the murder of Brian Wells -- a case that inspired Netflix's 'Evil Genius' -- isn't buying the shocking twist at the end of the documentary ... at least not most of it.
Dr. Jerry Clark -- who's heavily featured in the 4-part doc -- tells TMZ ... former prostitute Jessica Hoopsick's confession doesn't mesh with loads of evidence and investigatory work he did for years, so he doesn't believe she's credible.
If you haven't seen it, a big mystery of 'Evil Genius' is how much Wells knew about the bank heist that led to his death -- Jessica claims he knew nothing and she helped set him up ... but Jerry strongly refutes that and has some solid reasons.
Clark does agree with Jessica on one major component ... and 'Evil Genius' fans are going to want to hear his take on Marjorie Diehl-Armstrong and Bill Rothstein, too.
They should also check out what the director of the documentary, Trey Borzillieri, told us about Floyd Stockton.
FYI -- Clark spent 27 years in local and federal law enforcement, and retired from the FBI in 2011. He now teaches criminal justice at Gannon University.