Authorities have seized a 45-ton Panther tank, a flak cannon and other second world war-era military items in a raid on a 78-year-old collector’s home in northern Germany.

Birgit Hess, the prosecutor for Kiel, said the collector, whose name she would not release for privacy reasons, is being investigated for potentially violating German weapons laws but remains free while the probe is ongoing.

Investigators also seized a torpedo and multiple other military items in addition to the Panzer V “Panther” tank and the 88mm flak gun, Hess told the Associated Press. German military engineers were called in to haul the tank out of the underground garage of the house in Kitzeberg, near Kiel.

The flak cannon that was seized. Photograph: Carsten Rehder/AP

The collector’s attorney, Peter Gramsch, told the DPA news agency that all the items were properly demilitarised and registered. Hess said that she did not know whether the main gun on the tank could fire, but claimed it did not appear to be properly registered and that an independent expert said it was not properly decommissioned.

The collector came to authorities’ attention in an investigation into black market Nazi-era art that in May turned up two massive bronze horse statues that once stood in front of Adolf Hitler’s chancellery. Those were in the possession of another man, who maintains he is their rightful owner.

The tank owner has made no secret of his collection, openly talking about the tank and other items in media reports following the May revelation of the art investigation.

A neighbour, Kristin Schröder, told the Kieler Nachrichten newspaper that the man had fired up the tank during the particularly bad winter of 1978-79 and helped to clear snow in the area. “It was well known, at least to all the older Kitzebergers, that he had a tank,” Schröder said.