The day before Goldman Sachs announced its $2.2 billion purchase of fintech lender GreenSky, someone placed options trades that immediately soared in value, moves that market participants say indicates advance knowledge of the deal.

The market participants said that the trader bought 8000 options, which would pay off only if GreenSky prices rose to $10. The options were out of the money —  meaning that GreenSky was trading well below the strike price —  and cost just a nickel per share.

After news of the deal hit, the value of the contracts, each allowing for the purchase of 100 shares of GreenSky, skyrocketed. According to market sources, this trader saw a staggering 3,900% increase in one day. A $40,000 wager would have turned out to be worth $1.6 million.

Complex transactions such as acquisitions involve teams of lawyers, bankers and other experts with access to market-moving data. There are many people looking at a deal and information can often be lost. As many as one quarter of all public company deals result in some form of insider trading, often involving out-of-the-money calls in the options market, according to a 2014 study by professors at the Stern School of Business at New York University and McGill University.

Although there have been insider-trading cases ensnaring high-profile perpetrators, instances in which people used material, non-public information in the markets, most times the activity goes unpunished, according to the 2014 study.

Goldman Sachs did not respond to this article. A GreenSky representative didn’t respond to voice messages. The Securities and Exchange Commission and Financial Industry Regulatory Authority did not immediately respond to calls for comment.

Goldman was its own financial advisor and used Sullivan & Cromwell as legal counsel. JPMorgan Chase and FT Partners advised GreenSky, who also used law firms Cravath, Swaine & Moore and Troutman Pepper Hamilton Sanders.

GreenSky’s board also retained its own bankers and lawyers at Piper Sandler and Wilson Sonsini Goodrich & Rosati. Both banks and law firms did not respond immediately to messages or declined to comment.

GreenSky’s options activity is usually muted. The average daily volume of calls to GreenSky was less than 1000. Wagers in soon-to-be-profitable $10 call options surged over the last two weeks, however, indicating that it’s possible multiple traders had knowledge of the deal.

Jon Najarian (a CNBC contributor and veteran trader) said that volumes increased from 153 calls to 7 175 calls on September 7, to 9 calls by Sept. 9. Call volumes had reached 12,755 by Sept. 13, just two days after the announcement. According to Najarian, most contracts were sold on Sept. 15 for profit.

Najarian explained that “when we see such unusual activity we tend to assume that somebody has tomorrow’s paper today.” “None is so lucky. The person who bought these calls is likely to be questioned by regulators.

The trades were so brazen — with some of the calls set to expire in just days — that whoever made them must be inexperienced, according to a former Wall Street executive with more than four decades of markets knowledge. He suggested that regulators could be made to see the structure of these trades.

He said, “It looks like someone who was 22 years old and didn’t understand what they were doing.” But it was a simple fact that they were able to access insider information.

The financial columnist Matt Levine, a former Goldman banker who has written extensively about insider trading, has a few guidelines when it comes to the prohibited activity. His first rule (“don’t do it”) is followed by a second:

“If you have inside information about an upcoming merger, don’t buy short-dated out-of-the-money call options on the target,” Levine wrote in a 2014 column. The SEC will take you!

CNBC’s Bob Pisani contributes reporting.