Authorities arrested the man, who was not named, in Marburg, about 100 km (68 miles) north of Frankfurt, after contacting him on the so-called "dark net" and posing as buyers for an automatic weapon and another Glock 17 pistol for 8,000 euros ($9,021.60), it said.
The man's claims were supported by evidence gathered by the Munich prosecutor's office and Bavarian state police, the statement said.
It said the suspect was identified during an investigation into illegal weapons purchases by a 62-year-old accountant from the state of North Rhine-Westphalia and a 17-year-old student from the state of Hesse.
During the course of a subsequent sting operation, the suspect said he had sold the 18-year-old Iranian-German the Glock 17 pistol during a meeting in Marburg on May 20, followed by 350 rounds of ammunition during a second meeting on July 18. The gunman then went on to kill nine people in Munich, then shoot himself.
German Interior Minister Thomas de Maiziere last week announced a package of proposals - including the creation of a special unit to counter cyber crime and terrorism - to improve security in Germany after the Munich shooting and two attacks linked to the Islamic State militant group.
Munich guman Ali Sonboly. Picture courtesy: bild.de
Police on Tuesday arrested an armed 31-year-old German man who boasted during a sting operation that he had supplied the Glock 17 pistol used by the gunman who killed nine people in Munich on July 22, the Frankfurt state prosecutor said in a statement.
