The names of up to 2,444 police officers could be considered in connection with the Hillsborough disaster, it has been revealed.
Figures from the Independent Police Complaints Commission (IPCC) appeared before a Parliamentary committee to give details of the investigation.
It had been reported earlier that the names of 1,444 officers had been passed to the IPCC as part of the probe.
IPCC chief executive Jane Furniss said 1,000 more names are expected.
The Home Affairs Select Committee was also told Sir Norman Bettison's resignation as Chief Constable of West Yorkshire Police would not stop any investigation into his conduct after the tragedy.
The IPCC and the Director of Public Prosecutions are both conducting inquiries into the disaster.
Margaret Aspinall, chairwoman of the Hillsborough Families Support Group, said the extra names were "a real concern" as they could "delay everything for the families who are desperate to see closure on this".
"I am concerned where these extra names have come from - if there's another 1,000, have they found out something that we don't know about?" she said.
"If there were only 800 people on duty on that day, where have they all come from?"
The investigations were prompted by the Independent Hillsborough Panel Report, which found police and emergency services had made "strenuous attempts" to deflect the blame for the disaster - in which 96 people died - on to fans.
The independent panel revealed 164 police statements had been altered - 116 of them to remove or change negative comments about the policing of the FA Cup semi-final between Liverpool and Nottingham Forest at the Sheffield stadium in April 1989.
The panel also found that 41 of the 96 who had died had had the "potential to survive", and the attorney general asked the High Court to consider ordering fresh inquests into the deaths.
Earlier Home Secretary Theresa May had said she was talking to the IPCC about any extra resources needed to carry out the inquiry.
She said: "The government is determined to ensure proper investigations take place."