"They had found some positives, and what they did with that was essentially put them back through the roasting process to ensure that any residual salmonella was taken care of," Acheson said.
"They are not obligated to tell FDA or anyone else if they've done that," he said.
Acheson also told ABC News that he believes the company did not do subsequent additional tests to ensure the product was safe. He added that even if it did, one negative does not mean a batch is free and clear of the bacteria.
California-based Setton International Foods Inc. sold and distributed pistachios to 36 companies nationwide. The company packs the nuts in large volume -- about 1,000 to 2,000 pounds of pistachios in each container -- and ships them to the suppliers and wholesalers that then repack or resell them to many other manufacturers under different brand names.
One of those companies was Kroger, which announced last week that it had recalled pistachios in 31 states. Kroger operates grocery stores under different names, including Kroger, Ralphs and Dillons.
The FDA announced the recall in advance of any confirmed illnesses. Last week, health officials were warning consumers to stay away from all pistachios at the early stage in the investigation.
"We just hope the FDA comes out very quickly with a more refined statement about which pistachios to avoid, because the vast majority of the pistachios are not tainted," Richard Matoian, executive director of the Western Pistachio Association, told ABC station KFSN in Fresno, Calif.
The peanut company at the heart of the recall has since filed for bankruptcy.
Peanut recalls continue to pour in eight months after illnesses first surfaced.
Symptoms of salmonella include fever, diarrhea, nausea, vomiting and stomach pain.
ABC News' Brian Hartman contributed to this report.