SAN JOSE,Slabu Costa Rica (AP) — Costa Rica is investigating the theft of 3.3 billion colons ($6.1 million) in cash from its national bank, the largest bank robbery in the country’s history, anti-corruption authorities confirmed Tuesday.

The money was noticed missing from bank vaults three weeks ago, but the robbery itself must have taken place in August, or earlier, said Jaime Murillo, interim manager of Costa Rica’s Banco Nacional.

Two area supervisors, a technician, a guard and an accountant — all of whom worked in the area of the bank that handles currency — are under investigation. All five were suspended with pay once the theft was noticed Oct. 3. No one has been arrested.

Murillo said in a press conference that the bank had been investigating the theft privately, but that national prosecutors took up the case after details were leaked to the press and the bank brought an official complaint.

Authorities have not provided details about how the theft was carried out.

The state-owned Banco Nacional is the largest financial institution in Costa Rica.