Hillsborough: IPCC search for South Yorkshire police notes
Police notebooks from the Hillsborough disaster are being sought by the Independent Police Complaints Commission (IPCC).
The IPCC investigation is examining the deaths of 96 Liverpool football fans, in April 1989.
It said one officer interviewed wrote in their notebook on the day of the disaster "contrary to instructions" from commanding officers.
IPCC deputy chair Deborah Glass said no other notebooks have been recovered.
She said: "It has emerged at least one of the officers has advised that they did complete an entry in their pocket notebook from the day of the disaster, contrary to instructions given.
"As any such notebooks may prove to be a significant piece of evidence. We have instructed South Yorkshire Police to conduct a rigorous search of all their administrative storage areas."
An IPCC spokesperson explained that normal police practice was for officers to write in their "pocket books".
But officers were ordered not to on the day of the tragic FA Cup semi-final between Liverpool and Nottingham Forest.
The commission will have independent oversight of the search for the notebooks.
Last month, investigators found a further 55 police statements had been altered, in addition to 164 statements already identified.
An investigation by the Hillsborough Independent Panel showed police and emergency services had made "strenuous attempts" to deflect the blame for the disaster on to the fans.
Of the altered statements previously identified, 116 of them had negative comments about the policing of the match removed or changed.
The watchdog will review allegations surrounding amendments to statements, the actions of the police officers after the disaster and how West Midlands Police investigated South Yorkshire Police's conduct.
A separate team, led by former Durham Chief Constable Jon Stoddart, is investigating the response of all other agencies involved in the aftermath of the disaster.
Inquests into the deaths of the 96 victims are set to begin by 31 March at an unconfirmed location in the north west.
Verdicts of accidental death from the original inquest in March 1991 were quashed by the High Court in December.
The IPCC said preparations are ongoing for a witness appeal, expected to take place next month.