Two undercover policewomen and two undercover policemen entered the bar early that evening to gather visual evidence, as the Public Morals Squad waited outside for the signal. Once ready, the undercover officers called for backup from the Sixth Precinct using the bar's pay telephone. Stonewall employees do not recall being tipped off that a raid was to occur that night, as was the custom. According to Duberman (p. 194), there was a rumor that one might happen, but since it was much later than raids generally took place, Stonewall management thought the tip was inaccurate.