Belgian police on Tuesday released an old photo of a man carrying a military assault weapon, to try to solve the decades-old mystery of the country's bloodiest series of murders.
Known as the "Crazy Brabant Killers", the assailants killed 28 shoppers and wounded hundreds more in attacks on supermarket car parks in the Brussels area between 1982 and 1985.
Photographed in a forest, the man is wearing dark glasses and a military-style shirt and trousers and holds a semi-automatic combat shotgun made by Italian brand Franchi.
Federal investigators who took over the case more than two years ago are "committed to start from scratch", said spokesman Eric Van Duyse. The call for witnesses was part of that process, he added.
A tipster who claimed the man was "very important" handed over the photo to investigators in 1986, but never said anything more and nothing came of it, Duyse said.
Over the decades, investigators have considered various theories, including that the group was part of an attempt by the far left or far right to undermine the state.
The gang's equipment and ability in handling weapons raised suspicions at the time that there was a link to the Belgian security forces.
Investigators have also looked for links to local shooting clubs.
Van Duyse said investigators were taking another look at 3,000 names mentioned in the massive case file and had begun DNA testing for hundreds of them.
Belgian police say the photo was handed to investigators by a source who said only that the man pictured was 'very important' to the case