Spanish prosecutors announced fraud and other charges Thursday against 10 executives of two investment houses that guaranteed high returns on antique stamps — an alleged pyramid scheme involving billions of euros and some 350,000 small-time investors.

The executives worked for Afinsa and Forum Filatelico and five from each were charged. Both firms saw their offices in Madrid and other Spanish cities raided and shut down this week, drawing groups of distraught investors to the front doors, wondering about their savings.

Prosecutors allege that the stamps were marked up more than 1,000 percent.

Nine people have been arrested, including the five Afinsa executives charged Thursday and a stamp dealer who worked with the company and was also charged.

Of the 11 people charged, one Afinsa official remains at large, court officials said without explaining why.

The accusations stop short of a formal indictment, but allow authorities to keep the suspects in jail or under court supervision while the investigation continues.

Afinsa is the majority owner of New York-based auction house Escala Group Inc. Shares of Escala, which was known as Greg Manning Auctions until it changed its name last year, have taken a beating since Spanish police raided its and Afinsa's offices on Tuesday.

The accusations — including fraud, falsifying documents and mismanagement and in the case of Forum Filatelico, money laundering — were contained in documents released Thursday by Santiago Pedraz and Fernando Grande Marlaska, investigating magistrates at the National Court.

Two separate charge sheets signed by prosecutors specializing in corruption said both companies are now in a state of "absolute insolvency"

For years, Afinsa invited investors in many Spanish cities and towns to buy antique stamps "that were completely overvalued if not fake" and then paid them interest that did not come from appreciation in stamp value as promised but rather from money chipped in by new customers, the charge sheet says.

Forum Filatelico did the same things, except for using counterfeit stamps, the sheet said.

"In this way, the defendants designed a business that could only work if it repeated ad infinitum this same fraudulent practice with new customers," the prosecutors wrote, adding that apparently large sums of money also went to the defendants themselves.

Afinsa bought stamps from a supplier and sold them to investors at a profit margin of 1,150 percent, it said.

Investors bought sets of stamps from the companies on the promise of getting their money back at the end of a set investment period. Along the way, investors received interest payments as high as 10 percent a year — much higher than rates offered by banks these days for savings accounts or fixed-term investments.

The stamp collections were stored by the companies. In many case, the investors never saw their investments and knew little about them.

As of the end of 2004, Afinsa was holding $2.3 billion in money from 143,000, customers, the prosecutors said.

They did not give a figure for Forum Filatelico but news reports have placed it at $4.98 billion and 200,000 customers.

The Socialist government has said the investments are not covered by the kind of insurance that protects savings accounts in banks because these companies became unregulated in 2003 under a law passed by the previous, conservative government.