Three months after Dole Food began recalling its packaged salads from store shelves because of possible bacterial contamination, the company said Friday U.S. authorities are looking into the associated listeria outbreak.

“Dole has recently been contacted by the Department of Justice in connection with its own investigation, and we will be ... cooperating with the DOJ to answer questions and address any concerns,” the company said in a statement on its online site.

The criminal investigation is linked to a controversial food safety problem that forced Dole Food to shutter its plant in Springfield, Ohio, and recall numerous varieties of its packaged salads in 23 U.S. states and three Canadian provinces. The plant was recently reopened in a limited capacity, the company said last week.

The listeria outbreak was first detected last summer when 19 people, ages 3 to 83, in nine states fell ill because of the bacterial infection frequently linked to processed meats and vegetables. Overall, four deaths in the U.S. and Canada and multiple illnesses have been linked to the outbreak, according to the Wall Street Journal.

Late last month, the U.S. Food and Drug Administration declared the outbreak over. The FDA and the U.S. Centers for Disease Control and Prevention initiated an investigation in September that found genetic similarities between the bacteria in all of the cases. Their probe traced the source to the Ohio plant.

The criminal inquiry was launched because of suspicion that Dole Food executives may have had evidence of the bacterial infection at the plant as far back as July 2014, according to an FDA inspection report reviewed by the Journal. The report supposedly claimed the company failed to test surfaces at the plant for potential bacterial contamination.

Based in Westlake Village, California, the privately held Dole Food has grappled with six E. coli, listeria or salmonella outbreaks since 2005. A multistate outbreak in 2012 included one positive test for listeria in which no incidents of sickness were reported. All the outbreaks involved packaged salads.