The rise of cryptocurrency prices last year, including bitcoin, ethereum, and altcoins, could have been largely caused by price manipulation, according to a paper published today by researchers at the University of Texas at Austin. The paper, co-authored by a finance professor who is known for catching fraud in financial markets, reveals several distinct patterns in trading that suggest several people or a person at the major cryptocurrency exchange Bitfinex inflated virtual coin prices.

The 66-page report states that Bitfinex might have used the virtual coin Tether, which it owns, to generate fake demand for bitcoin by buying up the virtual currency and keeping its price up while it sank at other exchanges. The paper found that the more Tether entered the market, the higher cryptocurrency prices would rise, “similar to the inflationary effect of printing additional money.”

By using algorithms to analyze the millions of transactions listed on public ledgers, the researchers discovered that half of bitcoin’s price increase last year occurred hours after Tether was passed along to several other exchanges. Tether usually exchanged hands when bitcoin’s price was flagging.

Although the report can’t confirm price manipulation, it does point to suspicious patterns. Exchanges that had support for Tether saw the prices of coins like ethereum and Zcash rise higher than on exchanges that did not support Tether. And the report found that this year, after Bitfinex cut the supply of Tether short, the pattern ended.

Bitfinex is based in Hong Kong and is registered in the Caribbean, meaning that US authorities can only step in when investors from the US are involved in transactions, leaving much of it unregulated. But the geographic restrictions haven't stopped authorities from trying.

In December, the US Commodity Futures Trading Commission subpoenaed Bitfinex and the company Tether, after investors expressed concerns over these very same price manipulation issues. In January, reports of the subpoena began to surface, as did news that Tether had dissolved its relationship with an audit firm it had hired for an internal audit. Recently, Bloomberg reported that the Department of Justice is working with the CFTC to investigate bitcoin and price manipulation, although that investigation is still in the early stages.

There’s plenty about Bitfinex and Tether that has people raising eyebrows. Both Bitfinex and the company Tether have the same CEO, Jan Ludovicus van der Velde, although little else is known about him. While Tether lists Bitfinex as one of the main exchanges it’s integrated with, Bitfinex omits Tether from the dozens of cryptocurrencies on the front page of its website. Bitfinex did mention Tether in a 2015 blog post, but it did not mention any shared ownership at the time.

Tether claims that all of its coins are backed by US dollars held in reserve or other fiat currencies, although it hasn’t provided hard evidence to confirm this. Tether’s current market capitalization is $2.5 billion, according to CoinMarketCap.com.

Bitfinex did not respond to comment. It told The New York Times in a statement: “Tether issuances cannot be used to prop up the price of Bitcoin or any other coin/token on Bitfinex.”