While he was running for president, Donald Trump’s company nearly inked a deal to build Trump Tower Moscow.

It was a dream years in the making—and helped along the way by two New York real estate tycoons, one of whom is considered the right-hand man of an oligarch linked to an infamous money laundering investigation. Naturally, this man is also considered a friend of Vladimir Putin.

The two tycoons—Alex Sapir and Rotem Rosen—accompanied Donald Trump on his 2013 trip to Russia, where they reportedly tried to pull strings behind the scenes with to make Trump Tower Moscow a reality.

It’s yet another set of connections between Putin’s circle and Trump’s. And it’s of concern to Martin Sheil, a retired IRS criminal investigator, who told The Daily Beast that the links between the tycoons, their allies, and Trump are “all just very suspicious and raises a lot of questions.”

The Trump Organization did not respond to a request for comment. Rosen and Sapir could not be reached for comment.

Trump Tower Moscow negotiation efforts are likely within the scope of Bob Mueller’s probe. According to the authorization that Deputy Attorney General Rod Rosenstein signed appointing him special counsel, Mueller is authorized to investigate “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump,” as well as “any matters that arose or may arise directly from the investigation.”

So Mueller’s mandate is quite broad.

And it could ultimately include Rosen and Sapir, given that they traveled to Moscow with Trump for the 2013 Miss Universe pageant and the possible Trump Tower deal there.

Rosen is married to Sapir’s sister, Zina. Alex and Zina’s father was the late billionaire Tamir Sapir, who invested in the Trump Tower SoHo project and was accused of having mafia connections (accusations he consistently denied). Alex Sapir stepped in to take over the Sapir Organization when his father reportedly could no longer do so.

Rotem Rosen is a longtime associate of Lev Leviev, a Soviet-born Israeli billionaire who told The New York Times he views Vladimir Putin as a “true friend.” Leviev was also a partner in Prevezon Holdings, as Haaretz has noted. That’s the Russian company that was embroiled in a lengthy legal battle in the Southern District of New York over allegations that it laundered money into the U.S. in violation of the Magnitsky Act sanctions. Prevezon ultimately settled without admitting guilt, and paid out just $6 million. Natalia Veselnitskaya, the Russian attorney who met with Donald Trump Jr., Jared Kushner, and Paul Manafort last summer, also worked for Prevezon Holdings.

Rosen is Leviev’s right-hand man in the United States, according to Shturem.org, a site that covers the Hasidic movement Chabad (Leviev is one of the most generous supporters of the Chabad movement, as Politico has detailed). He formerly helmed the U.S. operations of Leviev’s Africa-Israel holding company.

And that link—between Rosen and Leviev—is what Sheil finds so troubling.

Because Rosen and Trump are connected, as well. When Rosen and his wife, the former Zina Sapir, had their first child in May 2008, they celebrated with a bris that made headlines. A picture on Shturem.org shows Ivanka Trump at the bris. New York Magazine reported that Donald Trump and Jared Kushner were also on the guest list.

Several months earlier, the pair had married at Mar-a-Lago. Donald Trump was one of the wedding’s 600 guests, according to Page Six.

Zina and Alex’s father, Tamir Sapir—now deceased—was a business partner to Trump, and invested in the Trump SoHo project. Alex joined his father Tamir, as well as Trump and his three oldest children, for the project’s launch on Sept. 19, 2007, as a Getty Images gallery shows.

Tamir was also a colorful character, to put it mildly. His first job in New York City, which he came to as an immigrant, was as a taxi driver. Later, he opened an electronics store which sold electronics wholesale to the KGB, as The New York Times reported in 2000. Sapir ended up becoming a billionaire real estate investor. And his rapid ascent to extraordinary wealth raised questions.

“They say I’m mafia, that I’ll be indicted for money laundering,” he told the Times. “It didn’t happen. Everything was done in the most legitimate way. No money laundering. No mafia.”

In 2009, he did plead guilty to a crime: that of violating the Endangered Species Act by smuggling rare animal carcasses into the U.S. on his yacht, according to Forbes.

And The Daily Beast reported in 2011 that Sapir’s former top aide pleaded guilty to racketeering, a crime he committed with members of the Gambino crime family (tidbit: Andrew Weissmann, now a top lawyer on Mueller’s probe, has experiencing prosecuting the Gambinos).

The web connecting Trump’s business interests to Russian billionaires is old and thick. That doesn’t mean he broke the law. But it may give investigators a lot to look at.