The South Yorkshire police officer in command of the 1989 FA Cup semi-final at Hillsborough did nothing to prevent the “inevitable” crushing of people on the Leppings Lane terraces after ordering an exit gate to be opened despite “an obvious and serious risk of death”, a jury was told.

Richard Matthews QC, opening the prosecution’s case on the trial’s third day at Preston crown court, took the jury through the moment when David Duckenfield agreed to the opening of exit Gate C to relieve potentially-fatal overcrowding which had built up outside the ground.

Duckenfield, who was promoted and appointed match commander shortly before the semi-final on 15 April 1989, is accused of a series of “extraordinarily bad” failures, amounting to gross negligence manslaughter, which led to the crush that killed 96 people.

These alleged failures, Matthews has said, included Duckenfield lacking detailed knowledge of the ground and how 24,500 people with tickets to support Liverpool would be admitted through the 23 turnstiles at the Leppings Lane end; a failure to monitor the numbers of people building up outside the “bottleneck” at the turnstiles, or to take any action, including delaying the 3pm kick-off, to relieve that buildup.

The jury has heard that due to changes from the identical FA Cup semi-final the previous year, between Liverpool and Nottingham Forest, 10,100 people with standing tickets at the Leppings Lane end had to be admitted through only seven turnstiles.

When Duckenfield finally agreed to open Gate C, having been warned that people would die outside if he did not, it was inevitable that the people allowed in would head for a tunnel facing them, which led directly to the overcrowded “pens” on the terrace, Matthews said.

“He [ordered the gate to be opened] having failed to take any action himself, or tasked anyone else with any action in good time, to prevent crushing to persons in ‘pens’ three and four, by the inevitable flow of spectators through the central tunnel. Not before, not during or after the five minutes or more that Gate C was opened, and the inexorable flow of more than 2,000 people through Gate C, did David Duckenfield do anything to prevent, to hinder, discourage the flow of people down the central tunnel, nor did he do anything to avert the inevitable result.”

Expert evidence to be given by an experienced structural engineer, John Cutlack, has calculated that in pen three, which had a “theoretical capacity” of 1,062 people, there were 1,430 people inside after the gate was opened. That escalated the risk of injury “into the realm of disaster”, Matthews said.

Of the period when the gate was opened, he alleged that Duckenfield’s failures continued: “Each was compounded by successive failures, each was contributed to by earlier failures and each was, and flowed from, his own decision-making and fell squarely within his personal responsibility as match commander.”

“Ultimately it will be a matter for you to decide,” Matthews told the jury, “but the prosecution allege that the evidence you will hear and see will demonstrate to you that these failings went beyond error or even serious error; they’re rightly to be viewed as extraordinarily bad – in the face of an obvious and serious risk of death.”

Colour footage of the crowd, shown to the jury, identified several of the 96 people who died in the crush. A survivor, Colin Moneypenny, Matthews said, would give evidence that he could not move because of the “intense pressure” around him and that he could feel a body underneath one of his feet. Another, Stephen Allen, an off-duty Metropolitan police officer, would describe “a scene of horror”, with a pile of six dead people on top of four who were semi-conscious.

The criminal charge of manslaughter against Duckenfield relates only to 95 of the people who died. The 96th victim, Tony Bland, suffered critical brain damage and died four years later in 1993, when life support in hospital was lawfully withdrawn. The law in 1989 stipulated that no charges relating to a death could be brought if the victim died longer than a year and a day after the alleged criminal acts.

Duckenfield and Graham Mackrell, the former Sheffield Wednesday secretary and safety officer at the time of the disaster who is accused of criminal breaches of safety legislation, have already pleaded not guilty in pre-trial hearings.

The case continues.