(CNN) Five companies are under investigation following the collapse of a Seattle crane that crushed cars on the street below and left four people dead -- including a college freshman and a retired city employee.

Washington State Department of Labor & Industries spokesman Tim Church said it may take up to six months to complete an investigation into the collapse.

"We expect we will likely need most if not all of that time," Church told CNN. "This allows us access to interview workers, access company records and perform other investigative work."

Church said the investigation into the companies is "part of the normal process when looking into a workplace safety incident," and does not suggest wrongdoing.

The crane fell from the roof of a building on Saturday. The building, which was under construction, was located on the new Google Seattle campus, CNN affiliate KOMO reported.

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