A mystery that has troubled Belgium for over 30 years may be solved after a deathbed confession by a former police officer that he was one of the "Crazy Brabant Killers", who left 28 people dead in a bizarre string of robberies in the early 1980s.

Officials on Monday confirmed reports that detectives have been working on the new lead for months and were optimistic about finally identifying the group, also called the "Nivelles Gang". Its bloody, three-year spree has long fuelled conspiracy theories involving right-wing plots and official cover-ups during the era of the Cold War.

With members dubbed "The Giant" and "The Killer", a getaway driver known as "The Old Man", and possibly other accomplices, the gang terrorised towns in Brabant province around Brussels. They staged over a dozen raids, often on supermarkets, sometimes barely taking petty cash but gratuitously gunning down customers, staff, and even children.

In 1985, after killing eight people at a store they burst into wearing grotesque face paint and disguises, they vanished as abruptly as they had appeared three years earlier.

At the weekend, a man told broadcaster VTM that his brother, a retired police officer in Aalst near Brussels, confessed to him as he lay dying two years ago that he was the tall man, suspected to be the ringleader of the gang, who came to be known as "The Giant".

"In the beginning, I was in denial because I really struggled with it," the unnamed man sobbed on camera.

"But today, I can say formally that this is my brother."

Newspapers published archive facial composites from the 1980s, "wanted" posters that once papered the country, along with off-duty snaps of the towering, bespectacled former special forces gendarme.

"I hope for the relatives of the victims that we can close this chapter soon," Interior Minister Jan Jambon said on Monday. Ministers have convened investigators to review the new evidence.

'Years of Lead'

A former Belgian legislator who took part in a parliamentary inquiry into the killing spree said suggestions of involvement by police officers were previously ignored by investigators. At the time, the killers' proficiency handling weapons and evading capture raised such suspicions.

Despite the possible identification, the motives of the gang remain unclear. Local media said the suspect was dismissed in 1981 from the Diana Group, an elite police commando unit.

The confession may revive suspicions about shadowy establishment support for the "Killers" during Europe's "Years of Lead", when left and right-wing urban fighters also troubled Italy, Germany and France.

Errors in the Brabant Killers case and, in the 1990s, the hunt for child-killer Marc Dutroux drove Belgium to replace a patchwork of forces with the federal police, which ministers credit with tracing the ISIL cell that struck Paris and Brussels.

But memories of past failures, including the oft-cited Brabant mystery, still provide ample material for critics of the police.

Among their crimes, the gang robbed a grocery at Nivelles in 1983, killing a couple who stopped at an all-night fuel station next door and then shooting a police who arrived at the scene.

In November 1985, they stormed into a supermarket in Aalst brandishing pump-action shotguns. The frenzied shooting of people cowering on the floor and a nine-year-old girl waiting in a car outside helped fix the gang's "crazy" image in the public imagination. But it was also their last.

Investigators believe the most murderous of the trio, the Killer, was hit by police and either died or was killed by the others, who then disposed of the body in a place where it was never found.