Three Minnesotans allegedly used food stamps from homeless people to buy thousands of dollars in soda and ramen noodles that were shipped to Liberia for resale, the first fraud of its kind in Minnesota that authorities can recall.

Investigators said Wednesday that they believe the criminal activity is far more extensive than what was uncovered in an 18-month investigation of the suspects, one of whom is a former state employee. Nevertheless, investigators were able to obtain enough evidence over a five-month period in 2012 to build a case and prosecute.

“I’m certain that we could have extended the investigation and we would’ve found more fraud, but at the end of the day, we wanted to limit it to that time period because that’s the time period we have corroboration from store video,” said Ramsey County Attorney John Choi.

On Wednesday, Choi’s office charged Noni S. Snider, 39, of Eden Prairie, and Walter C. Cooper, 38, of Plymouth, with wrongfully obtaining public assistance and conspiracy to commit a felony. Nyla J. Newburgh, 40, of Minneapolis, was charged with gross-misdemeanor conspiracy.

Snider declined to comment Wednesday. Several phone messages were left for Cooper, a former state employee who worked at a group home in Golden Valley. Newburgh could not be reached.

“This is the first case like this that we’ve seen,” said Jerry Kerber, Minnesota Department of Human Services inspector general. “One of the things we’re certainly very interested in is ensuring the public that there’s integrity to these programs.”

Kerber’s office assisted Choi’s investigators and other agencies in cracking the case.

According to the charges against the three:

In July 2012 the U.S. Department of Agriculture relayed a tip about the alleged crimes to Choi’s fraud unit. Using surveillance footage from a Wal-Mart in St. Paul and a Sam’s Club in St. Louis Park, investigators identified Cooper and Snider as primary suspects. The two have a child together. Newburgh also made some purchases for her personal use.

Authorities believe that Cooper and Snider made $11,502.25 in purchases between June and October 2012 using electronic benefit transfer (EBT) cards that Snider allegedly bought from homeless people for 50 cents on the dollar.

The 31 shopping trips outlined in charges show purchases ranging from as little as $49 to more than $1,100. Many of the purchases occurred at the Wal-Mart in St. Paul, but others were made at Sam’s Clubs in St. Louis Park, Maple Grove, Bloomington and Eden Prairie.

A Wal-Mart employee told investigators that Snider said the food was being shipped to poor people in Africa. However, the owners of a St. Paul storage unit being used in the scheme told investigators that someone they knew as “Walter” said he was shipping the goods for sale in a store in Liberia. Bank records showed nearly $27,000 in Liberian deposits.

Cooper founded Floxy Enterprises in 2008, allegedly so he could ship the goods to Liberia. Records from his work computer issued by the Minnesota Department of Human Services were key in cracking the case, charges show. The computer contained e-mails, invoices, bills of lading and shipping documents related to Floxy Enterprises.

Cooper worked as a human services technician at DHS from May 2, 2002, to Oct. 13, 2012, providing direct care to clients in hospitals and residential settings, said Karen Smigielski, spokeswoman for DHS. Cooper’s job had no involvement with the Supplemental Nutrition Assistance Program (SNAP), known as food stamps, she said.

Kerber said that his office investigates about 7,000 to 8,000 cases of EBT misuse a year, most of which are minor cases where a benefits recipient sells cards to someone who uses them to buy groceries. In fiscal year 2013, 259,000 households in Minnesota received SNAP benefits. 612-673-4482