Police say the driver didn't admit to emptying the contents of the bus’ septic tank into the river and onto the boat.
Police Commander Michael Chasen says video surveillance camera footage from nearby buildings shows the bus passing over the bridge, but police say there's no footage of waste being dumped.
More than 100 people on an architecture tour boat passed under the bridge and were showered with human waste.
Illinois' attorney general Tuesday sued the band over the incident and accuses the band's bus driver of violating state water pollution laws.
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