The Betancur administration in turn questioned the M-19's actions and its commitment to the peace process, as it continued to advance high-profile negotiations against with the FARC, which led to the creation of the Patriotic Union (Unión Patriótica) -UP-, a legal and non-clandestine political organization.
In May 1985, Liverpool were the defending European Champions' Cup winners, having won the competition after defeating Roma in the penalty shootout in the final of the previous season. Again they would face Italian opposition, Juventus, who had won, unbeaten, the 1983–84 Cup Winners' Cup. Juventus had a team consisting of many of Italy's 1982 FIFA World Cup winning team — who played for Juventus for many years — and their playmaker Michel Platini was considered the best footballer in Europe, being named Footballer of The Year by France Football magazine for the second year in a row in December 1984. Both teams were placed in the two first positions in the UEFA club ranking at the end of the last season and were regarded by the specialist press as the best two sides on the continent at the time. Both teams had contested the 1984 European Super Cup four months before, finishing with victory for the Italian side by 2–0.
At approximately 7 p.m. local time, an hour before kick-off, the trouble started. The Liverpool and Juventus supporters in sections X and Z stood merely yards apart. The boundary between the two was marked by temporary chain link fencing and a central thinly policed no-man's land. Hooligans began to throw stones across the divide, which they were able to pick up from the crumbling terraces beneath them. As kick-off approached, the throwing became more intense. Several groups of Liverpool hooligans broke through the boundary between section X and Z, overpowered the police, and charged at the Juventus fans. The fans began to flee toward the perimeter wall of section Z. The wall could not withstand the force of the fleeing Juventus supporters and a lower portion collapsed. Contrary to reports at the time, and what is still assumed by many, the collapse of the wall did not cause the 39 deaths. Instead, the collapse relieved pressure and allowed fans to escape. Most died of suffocation after tripping or being crushed against the wall before the collapse. A further 600 fans were also injured. Bodies were carried out from the stadium on sections of iron fencing and laid outside, covered with giant football flags. As police and medical helicopters flew in, the down-draught blew away the modest coverings. In retaliation for the events in section Z, many Juventus fans rioted at their end of the stadium. They advanced down the stadium running track to help other Juventus supporters, but police intervention stopped the advance. A large group of Juventus fans fought the police with rocks, bottles, and stones for two hours. One Juventus fan was also seen firing a starting gun at Belgian police.
Despite the scale of the disaster, UEFA officials, Belgian Prime Minister Wilfried Martens, Brussels Mayor Hervé Brouhon, and the city's police force felt that abandoning the match would have risked inciting further trouble and violence, and the match eventually kicked off after the captains of both sides spoke to the crowd and appealed for calm. Juventus won the match 1–0 thanks to a penalty scored by Michel Platini, awarded by Swiss referee Daina for a foul against Zbigniew Boniek.
The blame for the incident was laid on the fans of Liverpool FC. On 30 May official UEFA observer Gunter Schneider said, "Only the English fans were responsible. Of that there is no doubt." UEFA, the organiser of the event, the owners of Heysel Stadium and the Belgian police were investigated for culpability. After an 18-month investigation, the dossier of top Belgian judge Marina Coppieters was finally published. It concluded that blame should rest solely with the English fans.