German authorities have arrested four suspects in the theft of hundreds of ancient gold coins from a museum in Bavaria last year.

Thieves broke into the Celtic and Roman Museum in Manching and took 483 Celtic coins that were discovered during an archaeological dig nearby in 1999. The coins dated to around 100 BC.

Officials have said that cables were cut at a telecommunications hub and knocked out local networks before the heist, and that the thieves got in and out of the museum in nine minutes early on November 22 without raising the alarm.

Bavaria’s state interior ministry said raids were carried out in the Schwerin region of north-east Germany on Tuesday and four people were arrested.

The regional interior minister, Joachim Herrmann, said the operation was an “outstanding investigative success” and that “professional thieves” were arrested.