Two Colorado brothers who grew listeria-contaminated cantaloupe linked to a 2011 outbreak that killed 33 people nationwide and sickened hundreds more were criminally charged Thursday by federal authorities.

The Denver Post reports that Eric and Ryan Jensen, charged with four counts of introducing aldulterated food into the food supply, turned themselves in to federal marshals. They are scheduled to appear in court Thursday afternoon.

The outbreak two years ago this month was linked to Jensen Farms in Granada, Colo., after an investigation that traced half-eaten cantaloupe taken from patients’ refrigerators to grocery stores and then to the farm. The Centers for Disease Control and Prevention officially has linked 33 deaths to the outbreak, although 10 other people who had been infected with listeria bacteria after eating Jensen cantaloupe also have died since the outbreak.

The federal charges, announced by the U.S. Attorney’s Office in Denver, each carry up to one year in jail and a $250,000 fine.

“The charges against Eric and Ryan Jensen do not imply that they knew, or even should have known, that the cantaloupes had been contaminated,” said a statement issued by their lawyer. “As they were from the first day of this tragedy, the Jensens remain shocked, saddened, and in prayerful remembrance of the victims and their families.”

“This is an unprecedented thing, it’s not the norm,” said Amanda Hitt , an attorney with the Government Accountability Project, a whistleblower-supporting group in Washington, D.C. Hitt’s group favors more prosecutions in consumer cases when the evidence supports it.

Civil lawsuits by victims are not enough to persuade food companies to clean up, Hitt said. They build those costs into their plans with insurance and other measures. Prosecutions, she said, “could increase the security of the system and make a healthier system, and ultimately protect consumers.”

Food safety attorney Bill Marler of Seattle, who represents most of the victims of the listeria outbreak, praised the news but said prosecutors should consider going after the grocery stores and others.

“We will never have safe food from ‘farm to fork’ until the entire chain of distribution is held accountable for the food that they make a profit from.”

No public information had surfaced that Ryan or Eric Jensen knew they had any safety problems before cantaloupe was shipped to stores in the summer of 2011. Experts who have watched past food safety outbreaks said federal prosecutors do not usually pursue a case unless there is clear evidence that owners knew of or ignored obvious signs of contamination.