Owen Wilson wants nothing to do with a movie leaning into the idea O.J. Simpson was innocent of the infamous '94 murders -- turning down a boatload for the lead part.

The partially finished flick's director, Joshua Newton, admits he thought Owen was perfect for the role of attorney Douglas McCann, but he says even dangling a whopping $12 million check couldn't sway Owen to sign on the dotted line.

Newton tells Rambling Reporter talks initially went pretty deep with Owen about playing McCann ... a real-life attorney who got sucked into various conspiracy theories during Simpson's 1995 criminal trial.

He says they discussed it over lunch, his agent was all in and the paycheck was the cherry on top to sweeten the deal. But, apparently, Owen hadn't read the whole script at that point -- because Newton says the actor later dropped the bombshell ... "If you think I'm going to take the lead role in a movie about how O.J. didn't do it, you've got to be kidding me!"

While Newton's dream casting hit a major snag, he went on to find another person perfect for the role -- he hasn't revealed who it is yet, but actress Charlotte Kirk is reportedly playing Nicole Brown Simpson.

Goes without saying, Newton's still pushing to get this flick across the finish line by Oct 3 -- almost 9 years after it first started, and the 29th anniversary of Simpson's not-guilty verdict for the murders of his ex-wife Nicole and Ron Goldman.

Remember, Simpson was later found civilly liable for their deaths, and ordered to pay Nicole's estate and the Goldman family more than $33 million ... which, with interest, has ballooned to more than $100 million.