The Independent Police Complaints Commission was urged to make its inquiry into police malpractice over the Hillsborough disaster "as fast and as thorough as possible" at a memorial service to mark the 24th anniversary of the disaster on Monday.
Margaret Aspinall, chair of the Hillsborough Family Support Group, told a 7,000-strong crowd at Anfield that there could be no delay in the investigation into police conduct at the 1989 FA Cup semi-final between Liverpool and Nottingham Forest, when 96 Liverpool supporters died.
The IPCC inquiry followed the Hillsborough Independent Panel's report in September, which revealed the extent of the establishment cover-up and attempt to blame Liverpool fans for the tragedy. It is believed it could take two years to complete.
Aspinall, who lost her 18-year-old son James, said: "The truth has finally been revealed and now justice must follow… We [the families] are all getting older and some have been diagnosed with incurable illness. Delays are not acceptable under any circumstances."
Anne Williams, mother of 15-year-old victim Kevin, was diagnosed with terminal cancer just days after the panel's findings were made public. She was rebuffed by three attorney generals and the European court of human rights in her campaign for a fresh inquest, since granted, and defied medical advice to attend the service at Anfield.
Aspinall added: "The families here at Anfield are fortunate. Others have gone to their graves without seeing the truth exposed … That it took such a time-scale and numerous inquiries, when the evidence was always there, will forever be a stain on this nation and certain individuals. They know who they are."
Liverpool owner John W Henry and chairman Tom Werner were at the memorial for the first time, Henry giving a reading and praising the campaign: "I have been humbled by the dignity and perseverance of the families in their search for truth and justice," he said. "It is an honour to be here on this particular day, the first service since the publication of the Hillsborough Independent Panel's report. Now there is a real belief that justice will be served."
Everton chairman Bill Kenwright said: "They picked on the wrong city and the wrong mums. I hope by the 25th anniversary you will be celebrating the greatest victory any team in this country has achieved."