From the David Conn article in The Guardian. This was a tragedy just waiting to happen.
Duckenfield failed to do basic preparation for the semi-final. He did not study relevant paperwork, including the force’s major incident procedure, and signed off the operational plan two days after taking over, before he had even visited the ground.
He turned up to command the semi-final, he admitted, knowing very little about Hillsborough’s safety history: about the crushes at the 1981 and 1988 semi-finals, or that the approach to the Leppings Lane end was a “natural geographical bottleneck” to which Mole carefully managed supporters’ entry.
Duckenfield admitted he had not familiarised himself in any detail with the ground’s layout or capacities of its different sections. He did not know the seven turnstiles, through which 10,100 Liverpool supporters with standing tickets had to be funnelled to gain access to the Leppings Lane terrace, opened opposite a large tunnel leading straight to the central pens, three and four
He did not even know that the police were responsible for monitoring overcrowding, nor that the police had a tactic, named after a superintendent, John Freeman, of closing the tunnel when the central pens were full, and directing supporters to the sides. He admitted his focus before the match had been on dealing with misbehaviour, and he had not considered the need to protect people from overcrowding or crushing.