PODGORICA, Montenegro (AP) — Montenegro’s president called Thursday for a thorough investigation of whoever dug an underground tunnel into a court storage area in the country’s capital, describing the action as an an attack on the state and its justice system.

“I urge full responsibility and a full discovery,” President Jakov Milatovic said days after the tunnel was found leading from an apartment building to the Higher Court facility across the street in Podgorica.

Case files and tons of drugs and weapons seized during criminal investigations are stored in the depot, which is in the courthouse basement. Police suspect the brazen tunneling was an attempt by criminal groups to undermine cases by stealing evidence or to create a possible escape route from the courthouse.

“I hope it won’t be one of those cases when the public never get a full picture,” Milatovic said. “The tunnel is an attack on the justice (system) and on Montenegro.”

The tunnel was discovered Monday after court clerks noticed disturbed items and felt a draft in the storage area, Montenegrin media reported. Authorities have said the passageway was about 30 meters (33 yards) long.

It remained unclear if anything was missing. Montenegrin media said some weapons connected to a major criminal gang were stolen, but authorities have not confirmed the information.

Prosecutors said they were looking for six people suspected of digging the tunnel and had started questioning people in connection with the case, including the Higher Court president. The apartment where the tunnel originated was leased a few months ago, they said, without identifying the renter or giving any other details other than no one was inside the unit when they checked.

Montenegro’s police chief described the dig to the courthouse as a “movie-style” operation that took months to prepare and execute.

Some media reports about the discovery referred to high-profile prison escapes, including the one former drug lord Joaquin “El Chapo” Guzman made from a maximum-security Mexican prison in 2015 via a tunnel from his cell.

Located on the Adriatic Sea coast, Montenegro has been a key route for the smuggling of drugs into Western Europe through the Balkans. The country, which is a NATO member and a candidate for European Union membership, has pledged to fight crime and corruption.