Investors were promised big returns on real-estate investments.
Prosecutors say 2,300 victims were swindled out of $33 milion.
Retana was found guilty in January of six counts of mail fraud and one count of making false statements to government agents.
Retana's January trial took less than a week.
Jurors deliberated for less than an hour before returning a guilty verdict.
Retana began soliciting investors in 2006 through his company, Best Diamond Funding, by telling victims their money would be used to buy and sell real estate.
Retana guaranteed returns as high as 84 percent each year.
However, records show Retana used only a tiny fraction of the victims' money to purchase real estate, and that his company was actually losing money.
The victims who testified at trial were largely from working-class families in East Los Angeles.
During the course of the scheme, Retana collected about $62 million from approximately 2,300 victims who suffered actual losses of about $33 million.
Retana's scheme was almost uncovered in the summer of 2008 when the California Department of Real Estate audited his company.