Just two days after alleging that a South Florida man ran a “vast cash-to-Cuba operation,” federal prosecutors said they have no proof that the Castro regime is behind a multimillion dollar Medicare money-laundering scam.

But if the crux of a case filed in U.S. District Court is true — that a network of fraudsters funneled tens of millions of Medicare dollars to Havana — experts say there’s no way that much cash could wind up in bank accounts in Cuba without the government there knowing it.

So does check-cashing agent Oscar L. Sanchez’ indictment on a conspiracy to commit money laundering charge offer the first shred of substantiation to the long-held theory that the Castro brothers pull the strings behind elaborate plots to defraud Medicare?

Veteran Cuban analyst Maria Werlau said if the money indeed wound up in Cuba’s national banking system, “it is almost impossible to conceive that anyone not in the pay of Cuban intelligence would pour millions into Cuban banks.

“Who doesn’t know that all Cuban banks are Cuban government banks, i.e. under the total control of the state?” said Werlau, an anti-Castro activist who has studied the regime’s economy and illegal activities extensively.

Prosecutors have accused Sanchez, 46, of being the “financier” for a group that funneled $63 million of fleeced Medicare dollars into banks in Havana. His is the first such case that directly traced money allegedly ripped off from the federal healthcare program for the elderly to Cuba.

Prosecutors said the money linked to Sanchez — $31 million — moved through an intricate web of foreign shell companies before ending up in Cuba via Canada and Trinidad.

A motion filed Monday seeking to deny bond for Sanchez was unclear on whether the funds ultimately ended up in the Trinidad-based Republic Bank’s Havana branch, or in a bank that is run by the Cuban government.

IN DOCUMENT

The document did say that the alleged fraudsters’ Republic Bank accounts were opened at Republic’s branch office in Havana, “and that at least two of those accounts had standing instructions to the bank to wire all money immediately from the accounts to the Cuban banking system.’’

Werlau said Cuba has long faced allegations of laundering money for both drug traffickers and leftist terrorist groups. Accounts compiled by a series of defectors and other sources were bolstered in 2004 by a $100 million fine levied against a Swiss bank, which was caught buying and selling more U.S. dollars from Cuba than the dictatorship could justify having.

She added that no scam artist “in their right mind” would risk sending money to a country where the government has in the past frozen all foreign business accounts, suggesting that the suspected fraudsters were working for the Cuban regime.

But Florida International University law professor José Gabilondo said he was unconvinced by the prosecutor’s allegations, in part because Cuba charges steep fees on dollar transactions. Launderers who possibly diverted $63 million to Cuba would have lost 10 percent off the top.

“Why would they want to lose $6 million?” said Gabilondo, who has studied the Cuban banking system.

He said the motion prosecutors filed seeking Sanchez’s pretrial detention contained charged nationalistic language that seemed aimed to play on anti-Castro sentiments in Miami.