Back in 2017, John Griffin, a professor of finance at the University of Texas McCombs School of Business, noticed something strange. They were fascinated to see that a little-known token, Tether, that’s supposed to be backed one-for-one to the dollar was getting printed in large quantities. That clue led the pair to another: When new batches appeared, the price of Bitcoin seemed to jump. It looked like someone, or a group, was using that freshly printed “free money” to inflate Bitcoin’s price for their own profit.

In 2018, they coauthored a groundbreaking study showing that a single, still unidentified, Bitcoin “whale” almost singlehandedly drove the token’s giant run-up in late 2017 and early 2018 by distorting the trading in the token.

He believes it is happening again.

Toward the end of 2022, another mystifying trend caught Griffin’s eye. Despite the crypto crash and myriad other negative forces, every time Bitcoin briefly breached the $16,000 floor, it bounced above that level and kept stubbornly trading between $16,000 and $17,000. Almost unbelievably, as the crypto market has continued to unravel into 2023, Bitcoin has gone in the opposite direction, trading up 35% since Jan. 7 to $23,000.

“It’s very suspicious,” Griffin told Fortune. “The same mechanism we saw in 2017 could be at play now in the still unreal Bitcoin market.”

Update: It’s not like other cryptocurrencies are exhibiting strange behaviors either. Such as a Ether whale that dumped $41M just days before the market crashed.