Three women aged between 18 and 20 were killed in the "human avalanche" in the early hours of November 1st, 2012 at the Madrid-Arena venue, and two others aged 17 and 20 died later in hospital from their injuries. A further 16 people were injured.
The tragedy threw into turmoil the then city administration of Spain's governing conservative Popular Party as it was busy struggling to overhaul its finances in an economic crisis, and prompted deputy mayor Miguel Angel Villanueva to resign to restore "calm."
In the dock is Miguel Angel Flores, the owner of a private company that organised the event, as well as 14 other defendants in a trial that will last until May.
Flores has been charged with criminally negligent manslaughter and causing injury, accused of having "sacrificed security" for a "disproportionate" love of profit.
According to the indictment, some 23,000 tickets were sold for the event which took place in a venue that only had the capacity for 10,620 people.
The dance floor was so overcrowded that people could not move, "which caused a lot of distress... aggravated by the more or less advanced state of drunkeness of many present," it said.
"Some of the young people could not even breathe."
Many young people were in tears as they battled against a human tide for the exit doors in a panic apparently sparked by people throwing a flare and firecrackers, according to police and witnesses at the time.
Some of the exit routes were obstructed, and outside, police demonstrated "totally inappropriate passivity" given the large rave party that was taking place, the indictment read.
Disturbing amateur videos and photographs of the crush, which struck as the party's star DJ started his turn, showed partygoers piling on top of each other as they squeezed into a narrow corridor at the venue.
Spanish television broadcast recordings of calls by the distraught friends of injured victims to the rescue services, in which an operator told them ambulances were unable to reach the arena due to crowds around it.
Those running the city hall-owned company that managed the Madrid Arena venue, meanwhile, were accused of allowing the party to keep going until six in the morning even though two of the young women had already died.
The accused also include two men responsible for medical services at the party - a 77-year-old doctor whom witnesses said was overwhelmed when tragedy struck, and his 48-year-old son.