An investigation into claims that three New York City Police officers may have been intentionally poisoned while dining at a Shake Shack restaurant in lower Manhattan has found that no criminality occurred, police said Tuesday.

The officers were dining at the restaurant Monday evening when they discovered that a toxic substance, believed to be bleach, had been placed in their beverages, the citys police union said, later adding that they had been apparently poisoned.

The incident, however, may have the result of cleaning solution not being properly removed from a shake machine, CBS New York reported, citing unidentified sources.

The officers, who had been assigned to assist with ongoing protests, were taken to a hospital for treatment and released, authorities said.