The Independent Police Complaints Commission has released details about the response to its appeal for witnesses to assist the investigation into the aftermath of the Hillsborough disaster.

Within the first 48 hours of the witness appeal launch on September 17, more than 500 responses had been received. Investigators have already begun contacting some of those people who have responded to the appeal.

But the IPCC is keen for more people to make contact and knows eyewitnesses to the events on and after April 15, 1989 could now be anywhere in the world.

The IPCC is calling for witnesses who were at Hillsborough and gave their accounts to West Midlands Police, who carried out the investigation in 1989, to come forward.

The IPCC's criminal investigation is examining police actions following the stadium disaster. This includes how West Midlands Police conducted its inquiries.

It is known that thousands of members of the public gave witness accounts to West Midlands Police, either in writing, via telephone or in face-to-face interviews.

While our focus is on gathering evidence to assist with our investigation into West Midlands Police, the IPCC knows that some people have never given their account of what happened to them at Hillsborough to any previous inquiry. We want to give those people the opportunity now.

IPCC deputy chair, Deborah Glass, said: "We have had a very encouraging initial response to the appeal. I would like to thank everyone who has responded so far and all those who helped spread the news, in particular supporter groups and Liverpool Football Club.

"We want to speak to as many people as possible and I would urge people to contact us. We want to build the most comprehensive account there has ever been about the events of Hillsborough and we can only do that with the help of those who were there on the day and those who gave accounts previously to West Midlands Police.

"This is not simply a search on Merseyside for witnesses - this is a national and international search for witnesses. We are investigating events from more than 24 years ago and in that time people have moved, sometimes overseas. We want to reach out to them. We want to ensure everyone has a voice in our investigation.

"I know it won't be easy to revisit such incredibly traumatic events. We will support you through the process in whatever way we can. Eyewitness accounts will be vital in building the evidence base which would be crucial to any future prosecutions or misconduct proceedings."

You can find the IPCC's Hillsborough witness appeal at www.ipcc.gov.uk/hillsborough-witness-appeal. Anyone who cannot access the form and requires assistance can telephone on 0300 200 0003.

A video message from Deborah Glass can be viewed here.