A probe into the mysterious shooting of two soldiers has revealed the existence beneath the Serbian capital of a secret communist-era network of tunnels and bunkers believed to have served recently as hideouts for some of the world's most-wanted war crimes suspects.
The 3km2 complex -- dubbed a "concrete underground city" by the media -- was built deep inside a rocky hill in a residential area of Belgrade in the 1960s on the orders of communist strongman Josip Broz Tito. Until recently its existence was known only to senior military commanders and politicians.
The secret was revealed during an investigation this month into the deaths of two soldiers who were guarding an entrance to the complex when both were found fatally shot.
Official explanations of the Oct. 5 incident have failed to satisfy their families or a skeptical media, sparking speculation that fugitive Bosnian officers wanted by the UN for atrocities during the 1990s Balkans wars may have sought refuge in the complex behind 3m-thick concrete walls originally designed to resist nuclear attack.
"My son died because he saw some big secret," Petar Milovanovic, the father of one of the two soldiers, said recently. "They had to die to take the secret to the grave with them."
The army initially said the two soldiers shot each other, then backtracked and reported that one guard had murdered the other before turning his weapon on himself. An independent commission of experts has since been set up to investigate.
The circumstances surrounding the soldiers' deaths -- and any link with high-profile war crimes fugitives such as General Ratko Mladic -- remain murky. But the probe has shed light on a complex that was once so secret military men here say NATO didn't even suspect its existence when it conducted a bombing campaign against Serbia in 1999.
Tito, who ruled Yugoslavia from World War II until he died in 1980, ordered it built because he feared a nuclear attack by the Soviet Union after his country split in 1948 with the Eastern European communist bloc led by Joseph Stalin.
The entrance is hidden beneath an hilltop army barracks in Belgrade's Topcider district, which is home to several embassies and luxurious diplomatic residences.
According to media reports citing unnamed military sources, a 60m-deep elevator shaft leads down to a six-story underground complex dug into rock and reinforced by a 3m-thick layer of concrete.
Retired General Momcilo Perisic, who was the army's chief of staff until 1999, confirmed that the sprawling complex is intended as a wartime command center.
The main hall is as big as a subway station and could be used to shelter tanks and trucks, the reports by the Vecernje Novosti newspaper and other media said.
Tunnels stretching for hundreds of meters link palaces, bunkers and safe houses. Rooms are separated by steel vault doors 3m high and 30cm thick. The complex has its own power supply and ventilation.
Former Yugoslav President Slobodan Milosevic is believed to have convened his war Cabinet there while NATO bombs fell on his country for 78 days in 1999 to punish him for cracking down on independence-seeking ethnic Albanians in Kosovo.
The complex is so well designed that Yugoslav construction firms were reportedly hired by deposed Iraqi dictator Saddam Hussein to build a copy near his hometown of Tikrit in the 1980s.