A 32-year-old explosives expert for the German army, the Bundeswehr, is being questioned by police and had his house raided after he tried to mail a suspicious package, Germany's Spiegel magazine reported on Wednesday.

Customs officials at Frankfurt Airport raised the alarm after they discovered a Second World War-era machine gun silencer in a box the man was trying to ship to the United States.

Because the silencer is a piece of a prohibited weapon, investigators arrested the man on suspicion of violating the Foreign Trade Act.

Officials obtained a search warrant for the man's home in Aldenhoven, a suburb of the city of Düren in Germany's western state of North Rhine-Westphalia.

What did the investigation find? 

According to Spiegel, police discovered a cache of weapons, including guns from eastern Europe and ammunition used by Leopard 2 tanks.

However, the explosive elements of the items had been expertly removed. They were further rendered completely harmless by police bomb experts before being confiscated.

Investigators have not said whether they suspect any political motive behind the soldier's desire to build up an arsenal.

In recent years, the Bundeswehr has been hit by repeated scandals involving radicalized troops either belonging to far-right extremist groups or espousing extreme ideology.