A federal grand jury Thursday indicted James Bunchan, 52, a former marketing firm executive, on a charge of using the U.S. mails with intent to commission a murder-for-hire and soliciting a federal crime of violence.

He is in federal custody awaiting trial on past charges of mail fraud for an alleged investment scheme that bilked more than 400 mostly ethnic Cambodians in 15 states from about March 2002 to November 2005.

The latest federal indictment alleges that Bunchan mailed a letter from prison last June that offered an undisclosed sum of money to an undercover agent he thought was a hit man.

In return, Bunchan asked the hit man to kill Christian Rochon, a co-defendant also from Attleboro and also charged with mail fraud, and 11 Cambodian witnesses slated to testify in the fraud case, according to the indictment.

A third defendant, Seng Tan, has addresses in Attleboro and Quincy as well as Burnsville, Minn. Bunchan also has addresses in Quincy and Miami. In the fraud case, prosecutors allege the trio operated an Internet marketing firm and affiliate, and fraudulently solicited and secured investments in the two companies, World Marketing Direct Selling, also known as WMDS, and One Universe Online, that had offices in Attleboro, Canton and Boston. The defendants claimed the businesses marketed and distributed health supplements and other consumer products.

They told victims they would receive $300 a month for life, and the lives of their children, for every $26,000 they invested. Higher monthly returns were allegedly promised for higher investments.

Individual families were defrauded up to $620,000, and some took out home equity loans to invest, prosecutors say. The companies initially made payments to investors until sending out letters claiming technological problems were delaying payments.

The defendants spent most of the money on themselves, including Bunchan, who wrote up to $200,000 in checks to Las Vegas casinos in a single day, the attorney general's office has said.

Michael Bourbeau, who had previously represented Bunchan, said he would likely not continue as his lawyer. He offered no comment on the murder-for-hire indictment.

Rochon's lawyer, James Krasnoo, said he did not know if he, or the prosecutors, would be allowed to discuss the murder-for-hire indictment against Bunchan at the fraud case, when his client will stand trial with Bunchan and Tan.

The fraud case is scheduled to begin June 4 in U.S. District Court in Boston.