It is a murder mystery that gripped Belgium for decades and now, with the closure of the file on Friday, it may remain a cold case forever. A gang went on a murderous rampage between 1982 and 1985, killing 28 people including children in a series of supermarket robberies, becoming known as the “Crazy Killers of Brabant”. Outlandish theories have been offered to explain who was behind what local media called Belgium’s biggest criminal mystery of the last century. One thesis that was seriously considered was that it was an attempt to destabilise the Belgian state by current or former law enforcement officers close to the far right. Yet the case was never cracked. No one has ever been convicted despite multiple overlapping investigations, countless fingerprint and DNA searches, dozens of exhumations and even arrests leading to charges. On Friday, prosecutors finally gathered together the families of victims – still living without answers many years on – to let them know the case was being closed for good. “All possible investigative actions have been carried out,” Ann Fransen, the head of the Belgian federal prosecutor’s office, which took over the case’s various strands six years ago, told reporters in Brussels. “Unfortunately, we have not been able to bring the truth to the surface,” she said. “This means the case is now buried and it makes me very sad,” said Irena Palsterman, whose father was one of eight victims of a supermarket attack on 9 November 1985. One lawyer, Kristiaan Vandenbussche, alleged there had been a cover-up, accusing rogue law enforcement officers of “sabotaging” the investigation to protect the culprits. After the initial leads had gone cold, prosecutors picked up the case again in 2018 in after a TV interview by a suspect’s relative. The following year, charges were brought against a retired police officer suspected of hobbling the investigation back in 1986 by throwing guns and ammunition into a canal. But he was never convicted, and despite the efforts of a dozen police officers, prosecutors were forced to admit they had made no serious progress. It was not from a lack of trying, Fransen said. In all police had checked “1,815 pieces of information, both old and new”, looked at 2,748 sets of fingerprints and compared 593 DNA samples with those in the case file. They had exhumed “more than 40 bodies for research purposes”, she said. The mystery was all the greater since the relatively small sums involved – a total loot of 7m Belgian francs or about €175,000 (£148,000) – suggests money was not the motive for killing 28 people. Fransen conceded that closing the case would be a blow for the victims’ families, but said she felt it was necessary to be “clear and transparent” with them. The case will officially be closed after a procedural hearing to be held soon in Brussels, at which the families will have one more chance to request new avenues for investigation. Under Belgian law, there is no statute of limitations on the crimes involved.