In the end, it wasn't the security cameras or the audit inspections in the vault of Albania's central bank that brought down Ardian Bitraj.

It was the high blood pressure and lack of sleep, the burden of a multimillion-dollar secret.

Sitting down with his boss in July, Bitraj confessed his deception: Over a four-year period, he had stolen the equivalent of $6.5 million from the vault, covering his tracks by stuffing the empty cashboxes with books and balls of string.

The revelation brought down the central bank governor, led to the arrest of 18 employees and tarnished the reputation of an institution once lauded for its professionalism. And all for the sake of a gambling habit that led to massive losses, culminating in a series of fatal bets on the World Cup.

The full story of the Balkan bank heist is only just emerging, gleaned by Reuters in interviews with bankers, investigators and others involved, and from legal documents that include a transcript of Bitraj's confession.

It started in May 2010, when Bitraj, who had risen to become head of the cash processing department at the bank, first opened the metal and plastic clasps to the wooden boxes that hold its cash reserves in the cryptically named X Building on the outskirts of the capital, Tirana.

Bitraj, 45, had a penchant for placing bets on soccer matches, so about once a month he would wait for his co-workers to leave the room and swipe up to 2 million leks ($17,900), according to the confession.

Skewed cameras

Choosing carefully how he returned the boxes, Bitraj would make sure those he had tampered with were not in line for delivery to Albania's commercial banks, nor likely to be picked on in the regular random audit of the vault.

As the thefts mounted, he would stuff the boxes with packaging, balls of string and books to replace the weight of the cash.

All three keys needed to access the vault were kept in his personal safe. In statements to police, bank employees said they had not received any directive on how or where to store the keys.

Bitraj says auditors checked only 2 percent of the cash boxes in the vault. Fired governor Ardian Fullani says it was 5 percent, maintaining that checks in the country were comparable with other central banks in Europe.

Witness testimony has since revealed that the bank's plumber and electrician both made up the numbers for the required seven-member audit team in 2012 and 2013.

Oddly enough, according to Bitraj's confession, the security cameras in the cash processing section were not trained on the cashboxes, but on an office and anannex to the cash room.

Bitraj would stuff the money in a black plastic bag and place it in his office safe, investigators said. Then before leaving work, he would duck into the lavatory and strap the wads of bills to his body. His nephew would drive him home.

"The bank had no system to detect if anyone was carrying bank notes out, and some of the cameras were at an angle at which one could not see everything," said an investigator, who spoke on condition of anonymity.

The theft reached its peak during the World Cup in Brazil in June and July; at one point, Bitraj smuggled out $90,000 in a single day.

The strain on him was mounting.

His wife, in written testimony, said he was suffering from high blood pressure. Investigators said he was not eating properly, could not sleep and had stopped washing himself.

"I wonder why the guy didn't skip the country," said a veteran insider at the central bank.