If you've ever wondered what $20m (£16m, €18.6m) hidden under a mattress looks like, the US Attorney's Office in Boston has you covered. Federal officials posted a picture of the enormous stash of cash, hidden inside a cheap-looking spring bed, during a money-laundering bust on 4 January 2017 said to be related to a multi-billion-dollar Ponzi scheme.

"Photo of $20m seized in box spring following arrest of Brazilian national in scheme to launder proceeds of TelexFree", the prosecutor's office tweeted on Monday (23 January).

The wads of money were found inside an apartment in Westborough, Massachusetts as part of the investigation into a $3bn alleged fraud involving the internet phone service company TelexFree.

A 28-year-old Brazilian national, Cleber Rene Rizerio Rocha, was arrested and charged with one count of conspiring to money launder proceeds of the pyramid scheme following the raid.

The TelexFree scandal – described by prosecutors as the largest fraud of all time in terms of number of victims – is said to have resulted in around a million people across the world losing close to $1.8bn in total.

A long-running investigation into the firm saw federal agents search the company's headquarters in Marlborough, Massachusetts in April 2014.

The raid prompted Carlos Wanzeler, one of the company's founders, to flee to his native Brazil where he has since remained as a fugitive, prosecutors said. He was indicted in July 2014 with business partner and TelexFree co-founder James Merrill on charges that they operated the company as a massive pyramid scheme.

Merrill pleaded guilty to those charges in October 2016 to spare himself a possible 180-year prison sentence. He is awaiting sentencing but will serve no more than 10 years' imprisonment due to his cooperation with the government.

The arrest of Rocha, and discovery of the $20m, came after an extraordinary operation plotted by investigators that managed to foil alleged attempts by Wanzeler to bring millions of dollars of TelexFree money – still hidden in the greater Boston area – from the United States to Brazil. It saw an associate linked with Wanzeler, and tasked with helping launder the cash through Hong Kong to Brazilian accounts, turned by investigators into becoming a cooperating witness, prosecutors said.

"Rocha met the cooperating witness at a restaurant in Hudson, Massachusetts, and allegedly gave him $2.2 million in a suitcase," prosecutors said in a statement. "After the meeting, agents followed Rocha to an apartment complex in Westborough, Massachusetts, and later arrested him. That night, federal agents searched an apartment at the Westborough complex and seized a massive stockpile of cash hidden in a box spring. The cash appears to total approximately $20 million."

According to an affidavit filed in Rocha's case, he arrived at JFK Airport on New Year's Eve telling customs officials that he was visiting New York for his honeymoon, the Boston Globe reported.

When he was arrested, he "admitted his role in the operation, telling the agents that he travelled to the United States to facilitate the money transfer on behalf of [Wanzeler's] nephew and Wanzeler," the court filing reportedly said. Rocha faces substantial prison time if convicted of the conspiracy count.

"The charging statute provides for a sentence of no greater than 20 years in prison, three years of supervised release and a fine of $250,000 or twice the gross gain or loss, whichever is greater," prosecutors said.

"Actual sentences for federal crimes are typically less than the maximum penalties. Sentences are imposed by a federal district court judge based on the US Sentencing Guidelines and other statutory factors."