A former police officer has been arrested on suspicion of concealing evidence in the unsolved case of the “Crazy Brabant Killers”, a gang who murdered 28 people in Belgium, including children, in a series of raids and robberies in the 1980s.

During a three-year crime spree, supermarkets, jewellers, bars and hostels were raided by the group – usually comprising three disguised men wearing face paint known as “the Giant”, “the Killer” and their getaway driver, “the Old Man”.

Their haul was often of limited value but the French-speaking group became known for casually shooting dead customers, staff and even children without mercy, taunting and shouting at their victims.

The gang, named after the province in which they were most active, suddenly ceased their activities and disappeared in 1985, prompting countless theories about their identity and motives.

A retired police officer, named only as Philippe V, was arrested on Wednesday and is reportedly expected to appear in front of an investigatory judge on Thursday. He was a member of the Belgian police’s Delta group, which had been investigating the gang in the 1980s.

He has been questioned in relation to his role in the November 1986 discovery in a canal of a bulletproof vest, a firearm stolen from a police officer and ammunition.

Eric Van Der Sypt from the federal prosecutor’s office said a previous search of the canal a year before had not yielded anything.

Forensic research, published in 2013, suggested the items could have been thrown into the water a few weeks before the police found them.

“It is clear that when you dive in 1985, you cannot find anything,” Van Der Sypt said. “When we dive again in 1986, we find a lot of objects, which is not normal.”

A spokesman for the prosecutor’s office said the former officer had been questioned on suspicion that he had “retained at least certain, possibly crucial, information”.

Walter Damen, the former officer’s lawyer, told the Flemish TV channel VRT his client denied any allegations of wrongdoing.

“He says that he did not influence the investigation at all, that he had no contact with the band of Brabant killers … In January 2019, he is asked for information on November and December 1986. It is difficult, because [to] each sentence must be added ‘I think’ or ‘I do not know’,” Damen said.

Due to the killers’ proficiency in handling weapons, suspicions were raised at the time of the murders of a link with a now disbanded paramilitary police force.

There were also rumours they were part of an attempt by the far left or far right to undermine the state, a theory the Belgian government recently said remained a possibility.

In 2017, the brother of a retired policeman in Aalst, west of Brussels, came forward to claim his dying sibling, Christiaan Bonkoffsky, had confessed to being “the Giant”. The federal prosecutor’s office said last year they were convinced this was not the case.

The gang’s final crimes took place in November 1985, when they burst into a supermarket in Aalst firing pump-action shotguns. Eight people were killed in the raid, including those cowering on the floor and a nine-year-old girl waiting in a car outside.

It was believed at the time that “the Killer” was fatally wounded by police in the raid, although his body was never recovered.