Tim Vander Tuuk reporting.

(Waukegan, IL)  Waukegan Fire officials have concluded their investigation into a plant explosion that killed four people.

Authorities say while the have ruled out an intentional act, and know the point of origin for the explosion, they may never know the exact cause.

The incident took place back on May 3rd at AB Specialty Silicones.

Waukegan Fire says while they haven’t been able to draw an official conclusion, several other local, state and federal agencies are continuing to look into the blast, and may come up with more answers.