BOSTON - A former Attleboro couple was sentenced to a combined 55 years in prison Thursday for operating an illegal pyramid scheme that defrauded almost 500 victims of about $27 million.

Prosecutors said James Bunchan, 57, of Quincy, Attleboro and North Miami Beach, Fla; and his wife, Seng Tan, 61, of Quincy, Attleboro and Burnsville, Minn., used their Cambodian ethnicity to solicit funds from Southeast Asian immigrants.

U.S. District Judge Richard G. Stearns sentenced Bunchan to 35 years and Tan to 20 years in a federal prison for conspiracy, mail fraud and money laundering.

"The defendants ran a large pyramid scheme that preyed primarily on ethnic Cambodians," U.S. Attorney Michael Sullivan said. "The victims are hard-working people who were led to believe that they were making safe and responsible investments. Sadly a number of these victims are now facing the loss of their homes and financial ruin."

According to evidence presented at their trial, Bunchan, Tan and a third person, Christian Rochon, 54, of Warwick, R.I., were the heads of two companies, WMDS, also known as World Marketing Direct Selling, and One Universe Online, also known as 1UOL, with offices in Canton, Attleboro and Boston. Between October 2000 and November 2005, Bunchan, Tan and Rochon solicited investments in the two companies, which sold and distributed health supplements and other consumer products.

Investors were told that their lump sum investments, usually in units of $26,000, would yield a $300 monthly payment for life that could be passed down to their children.

At first, prosecutors said, the trio made the promised payments, leading many of the original investors to recruit additional victims. For the most part, however, the trio spent the money on a lavish personal lifestyle, including luxury cars, Las Vegas and Bahamas trips and more than $6 million in gambling at casinos.

When the scheme collapsed, prosecutors said, the defendants attempted to intimidate investors by threatening lawsuits.

At the sentencing hearing, the prosecutor noted that Bunchan attempted to hire a hit-man to murder potential witnesses. Bunchan has been charged separately for that offense.

Rochon will be sentenced at a subsequent hearing.