The Washington Post reported Sunday that the Trump Organization had spent more than $400 million in cash acquiring properties, often without taking on any debt at all, beginning in 2006. The president’s son Eric Trump told the Post that the simple explanation was that Trump properties threw off so much cash, there was no need to borrow.

Even if true, experts agree: That’s weird. Real estate buyers usually like to spend as little of their own cash as possible. Big purchases often come with massive loans—like the $1.2 billion mortgage Kushner Cos. took out on its flagship 666 5th Ave. skyscraper when the president’s son-in-law purchased the building in 2007. This was especially true of Donald Trump, a self-styled “King of Debt” who managed to escape disaster in Atlantic City, New Jersey, in part because so little of his own money was invested in the casinos he ran there. And never has it been more true than during the past decade, a period during which historically low interest rates made borrowing money cheaper than ever.

There are a few reasons a company might want to buy entirely with cash. Trouble with lenders is one of them. Cash purchases are important if you need to move quickly, something you see with money going into red-hot housing markets like Silicon Valley and out of insecure economies like China and Venezuela. And then, of course, there is the reason that the president’s former chief adviser, Steve Bannon, told Michael Wolff was at the center of the Mueller inquiry: money laundering.

Claims of money laundering have long swirled around the purchases made at Trump properties. In November, Fusion GPS founder Glenn Simpson—whose firm researched Trump at the behest of the conservative Washington Free Beacon,* and later hired Christopher Steele to produce the now-infamous opposition research dossier—told a House panel that the firm saw condo sales in Trump buildings that “were suggestive of money-laundering.”

Time was money got laundered through such cash-intensive businesses as convenience stores, restaurants, parking garages, and retail. The basic idea is this: If you have a suitcase with $1 million in drug trade profits and you have a pizza place that makes no money, you tell the IRS the pizza place made $1 million, and you empty the suitcase into the cash register. Dirty money made clean through pizza. Or, in the case of Baltimore drug kingpin Avon Barksdale in The Wire, a photocopying business.

As Avon’s consigliere Stringer Bell realized, however, real estate can make a superior vessel. An investigation by BuzzFeed News found Trump buildings attracted an enormous number of all-cash purchases by shell companies, two characteristics considered red flags for money laundering. In a hypothetical money-laundering condo purchase made by a shell company, a buyer would endow an anodyne-sounding LLC with profits from illicit proceedings—cocaine trafficking, for example. Two years later, the LLC sells the property to any old joe, and the money—which is now “clean,” sourced from a legitimate real estate transaction—can be deposited into a U.S. bank account or wherever else its owner wants to put it.

The scheme often works because there’s a lot of noise around this signal. A ton of people make all-cash, LLC-backed purchases for perfectly legitimate reasons: because they’re making an investment, or because they want to move money from a risky environment (Venezuela, China) into a “safe haven” like New York or London. They use an LLC because they want privacy—an increasingly common tactic among landlords of all kinds in the United States.

Mixed in with those purchases is an undetermined degree of money laundering.

“Real estate agents, lawyers, title insurance companies—virtually all of the major players in a real estate transaction other than the banks are not covered by anti–money laundering compliance rules,” explains Ross Delston, a lawyer and money-laundering expert in D.C. “Criminal laws, of course. But not what’s called preventive measures, which banks and a whole panoply of financial institutions are covered by. What this means is that if the source of the money is an illegal activity, and if a criminal or intermediaries used by that criminal can move money around enough, put it in real estate, and even sell it as a loss, in general the money has been laundered.”

Not taking on debt from a regulated lender, in short, can remove an entire layer of scrutiny from the acquisition process. (Banks have to abide by so-called customer due diligence regulations, which were put in place as part of the USA PATRIOT Act.) There are other reasons property has become a popular money-laundering vessel: It’s easier to find a condo than to find a front. At least in the U.S., real estate tends to be a good investment in and of itself. It has been immune from regulatory attention paid to “front” businesses. Finally, the increasing globalization of real estate has made these purchases both easier to make and less likely to stand out.

Last year, the golf writer James Dodson recounted to WBUR a 2013 game with Donald and Eric Trump in which the younger Trump told him the company’s burst of golf courses was funded by golf-loving Russians. Here’s the relevant portion of his recollection, which Eric Trump has denied:

“So when I got in the cart with Eric,” Dodson says, “as we were setting off, I said, ‘Eric, who’s funding? I know no banks—because of the recession, the Great Recession—have touched a golf course. You know, no one’s funding any kind of golf construction. It’s dead in the water the last four or five years.’ And this is what he said. He said, ‘Well, we don’t rely on American banks. We have all the funding we need out of Russia.’ I said, ‘Really?’ And he said, ‘Oh, yeah. We’ve got some guys that really, really love golf, and they’re really invested in our programs. We just go there all the time.’ Now that was [a little more than] three years ago, so it was pretty interesting.”

If you were a Russian investor, buying golf courses would be an extremely strange way to launder dirty money, at least under any conventional understanding of how that works. In part because doing anything else with that money—buying tens of millions of dollars worth of real estate in New York City, for example—would be very easy! But bringing your money to a corporation to buy a golf course isn’t really a property investment at all—it’s a loan to a company that claims to throw off millions in profits each year.