Griffin isn’t convinced by Cboe’s explanations. “There is no doubt we understand how the market works,” he says. Meanwhile, he fears the VIX paper turned into a how-to guide for would-be manipulators. He says people at banks, whom he wouldn’t identify, contacted him asking for the appendix to the paper, which describes in detail how the suspected manipulation could work.

https://www.bloomberg.com/news/articles/2018-10-12/this-texas-finance-professor-sifts-data-for-signs-of-rigged-markets?srnd=premium