Japanese police are continuing to investigate the factory and workers at Maruha Nichiro Holdings' in Gunma prefecture in connection with the contamination of around 6.4 million bags of frozen food with the pesticide malathion. The products were found to contain up to 2.6 million times the permitted levels of the chemical.

Prefectural health officials referred the matter to police after finding no evidence of contamination during production at the facility. Police say they will continue to investigate the facility as well as interview workers.

Maruha Nichiro has come under scrutiny for not regularly testing products for contamination or adulteration. “We test products several times a day for evidence of spoilage, based on the law, but we had no reason to believe pesticides would be present, so we didn’t test for that,” Ichiro Gohara, a spokesman for the company, told reporters. “Until now, we haven’t received any reports of problems.”