Rockford police suspect a warehouse destroyed in a fire this week was the site of a marijuana growing operation.

Deputy Police Chief David Hopkins says they had received a tip, but were not able to substantiate it before Tuesday's fire destroyed the building.

The Rockford Register Starreports that no arrests have been made.

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Authorities still don't know what caused the fire, which broke out around 1:30 a.m. Tuesday at the former Asher Tool and Machines Sales warehouse.

It is not known whether the fire was intentionally set, perhaps to destroy evidence, or whether it was accidental.

Another fire, on Monday, led to the discovery of a marijuana operation at a residence. No arrests have been made in that case either and Hopkins says no connection has been determined.