South Yorkshire Police, Sheffield Wednesday football club, Sheffield City Council and the Football Association are being investigated for possible criminal culpability over the Hillsborough disaster, in which 96 Liverpool fans died.

The disclosure was made by the senior detective leading an investigation into the tragedy at the stadium in Sheffield on April 15, 1989.

Jon Stoddart, former chief constable of the Durham force, told the Guardian that all four organisations were being investigated for possible gross negligence manslaughter. He said: “We are exploring all liability, both public and individual. We are looking at unlawful killing; who is responsible for the deaths.”

He said more was being looked at than command and control of the crowd.

“It is about the safety of the stadium, certification, the planning and preparation, the engineering and design that went into the Leppings Lane end (where the people died),” Stoddart said.

The club offered to host the match despite serial breaches of the Home Office guide to ground safety and a safety certificate 10 years out of date, the newspaper said, while the council was statutorily responsible for licensing the stadium as safe, and the FA commissioned the ground for the FA Cup semi final despite Hillsborough’s safety breaches and previous crushes at semi-finals there in 1981, 1987 and 1988.

Meanwhile it has emerged that more than 90 police pocket notebooks that could contain crucial new information about the disaster have been recovered by investigators.