"Maybe things wear on you after while," Bennett said.
Authorities have released few details about the attack, including the names of the shooter and victims. The facility was locked down temporarily, and police asked motorists to avoid the area near Highway 67 south of Interstate 94.
Officers from several area agencies were on the scene.
The Roundy's complex employs close to 1,000 people, according to the Journal Sentinel. Roundy's is a subsidiary of Cincinnati-based Kroger that operates Pick 'n Save and Metro Market stores in Wisconsin and Mariano's grocery stores in northern Illinois.
In a statement, Roundy's said, "We are deeply saddened by the incident that occurred last night at our Oconomowoc distribution center.