The federal fraud trial of a former Minnesota Viking and his business partner began Monday with a debate over how one of the defendants viewed his investors.

Prosecutors say Jeffrey Gardner swindled clients, whom he called his "Ma and Pa Kettles," out of $25 million in a scheme in which he used their money to pay down debts instead of making promised real estate investments.

Stu Voigt, a former NFL tight end who appeared in three Super Bowls for the Vikings before embarking on a career in business, is also charged in connection with alleged criminal activity while serving as chairman of a Bloomington bank.

"This case is about gambling with other people's money," Assistant U.S. Attorney Kimberly Svendsen said during opening statements in U.S. District Court in Minneapolis.

Gardner and Voigt are standing trial on a slew of federal fraud charges: Gardner faces four counts of mail fraud and one count of conspiracy to commit mail fraud, while both he and Voigt are charged with four counts of bank fraud and three counts of false statements in a loan application.

Andrew Birrell, one of Voigt's attorneys, told the Star Tribune last week that everything Voigt did "was in good faith" and that he "lost all his money." Gardner's attorney, James Ostgard, said Gardner's business — and its investors — was simply one of many to fall victim to the Great Recession.

Over the course of theventure, which allegedly spanned from 2005 to 2008, Gardner regularly called his investors the "Ma and Pa Kettles," a reference to a 1950s film couple, Svendsen said.

Ostgard called it a term of affection. He said Gardner, who built his companies "over the course of a lifetime" after a blue-collar upbringing, could see himself in many of his clients.

But Svendsen painted a vastly different picture, saying Gardner intended the term as a derogatory reference to the "unsophisticated" nature of many of the investors.

As Gardner's Hennessey Financial LLC was failing, she said, he continued to mail updates to his clients suggesting that investments would still yield promising returns.

Ostgard said those mailings outlined the risk involved in such investments. He also suggested that the blame for the investors' peril should be directed at Todd Duckson, a Twin Cities attorney who was found guilty of securities fraud in 2013 for his role in advising a hedge fund that was created to lend money to Hennessey Financial.

But Svendsen said Gardner's scheme began before starting working with Duckson. Svendsen also said Voigt and Gardner didn't disclose that Gardner owed Voigt nearly $3 million when Gardner was applying for a line of credit from Bloomington-based First Commercial Bank, where Voigt was chairman.

Voigt continued to receive healthy commission payments each time he brought in new investors, she said.

Svendsen told jurors they will hear complicated information during the trial, but argued that the heart of the government's case is simple.

"It's about Jeffrey Gardner and Stu Voigt putting their own interests ahead of their duty to tell the truth," she said.

Stephen Montemayor • 612-673-1755

Twitter: @smontemayor