Solution

Tom Dietz put the cholera bacterium in Adler Foods Chicken soup and put them back on store shelves. He was getting revenge on Owen Adler for causing him to lose his farm.

Monte Evans investigated the New Leaf Foods case In 1997 and found that the company was responsible for the contamination of the soup. That is why his fingerprint appears on the document. The illnesses were caused by staphaloccocus infection which resulted from unsanitary conditions in the factory. Owen Adler, owner of Adler Foods, paid Monte Evans a large sum of money to alter the Investigation Report Form to make it look like Dietz Farms' chickens were the cause of the contamination. Monte changed the form to say that salmonella was the contaminating agent. He also forged Johnathan Pahl's signature and covered his name with Amos Barreto's name so that he would not be connected to the scam if anything went wrong.

Tom Dietz figured all of this out and got revenge on Owen Adler by contaminating the soup with Cholera, which he got from the lab at Glaxo-Wellcome where he works.