A U.K. watchdog has launched its biggest-ever investigation into police actions, opening a new inquiry Friday into the 1989 Hillsborough stadium disaster that left 96 fans dead and whole communities angry over a decades-long police cover-up.

The Independent Police Complaints Commission said a large number of serving or retired officers would be investigated over what happened on April 15, 1989 — the day that officers herded around 2,000 Liverpool fans into caged-in enclosures that were already full during an FA Cup semifinal between Liverpool and Nottingham Forest at the stadium in Sheffield, central England.

Dozens died amid the crush, many due to lack of attention from police and emergency services. Suggestions from police and the press that drunken fans themselves may have been responsible also led to a poisonous legacy of hurt, suspicion, and mistrust.

Commission Deputy Chair Deborah Glass acknowledged Friday that the investigation had been a long time coming, saying that two decades was "far too long to wait" and speaking of a "generation of distress and anger."

"Justice demands that we do whatever is possible to investigate culpability for any offence that may have been committed, and to do so thoroughly and fairly," she said in a statement. "I want to give them my assurance that we will do everything in our power to investigate these serious and disturbing allegations with the careful and robust scrutiny they deserve."

The deaths at Hillsborough shocked the country and helped transform U.K. sports. It led to the introduction of all-seated soccer stadiums for elite clubs, making games more family-friendly and, eventually, helped to drive out the hooliganism that had long tainted British soccer.

A government-appointed panel recently confirmed that police bungling led directly to the disaster and that dozens of injured fans were denied medical treatment that could have saved their lives.

Glass said her commission would examine whether police fed disinformation to the media, lawmakers and other investigators "in an apparent attempt to deflect blame from the police on to the fans."