Brian Hartman of ABC News is reporting that investigators have linked at least three different kinds of E. coli to Nestle’s cookie dough but they remain stumped as to just how the bacteria got in the product.

DNA testing of E. coli found in an unopened package of cookie dough at Nestle’s plant in Danville, Va., determined the genetic fingerprint of the E. coli found at the plant is different than E. coli that has been linked to a 30-state outbreak that has sickened at least six dozen people, and that an altogether different strain of E. coli was found in dough recovered from the home of a victim.

Dr. David Acheson, the Food and Drug Administration’s assistant commissioner for food safety said,

“The investigation is winding up. It is not exactly over yet. But we have not figured out the likely ingredient. … It is unlikely that we will ever make a final determination of how this contamination occurred. … Theres no indication that this was deliberate.”