OSAKA -- Osaka prosecutors on Thursday searched two more Snow Brand Milk Products Co. offices in connection with a mass outbreak of food poisoning last summer caused by milk products made at its Osaka plant.

The Osaka District Public Prosecutors Office carried out the search of the company's Tokyo headquarters and Osaka branch office on suspicion of negligence resulting in injury and death.

The prosecutors said data related to an internal network that relayed information to top officials will help determine whether it is possible to substantiate the charges.

On Wednesday, prosecutors searched the company's Sapporo headquarters and the Tokyo home of former President Tetsuro Ishikawa, 67.

Police on March 16 sent papers on nine officials, including the president and former Senior Managing Director Hiroshi Soma, to prosecutors on suspicion of professional negligence in the food poisoning, which left one Nara Prefecture woman dead and 13,000 people ill.

The Osaka plant that produced the milk and yogurt that caused the poisoning was shut down Jan. 31.