 Led by Colonel Thomas E. Rose of the 77th Pennsylvania Infantry, the prisoners started tunnelling in a rat-infested zone which the Confederate guards were reluctant to enter.The tunnel emerged in a vacant lot beside a warehouse, from where the escapees could walk out through the gate without arousing suspicion.Since the prison was believed to be escape-proof, there was less vigilance by the authorities than in other camps, and the alarm was not raised for nearly 12 hours.