The eight detainees, as well as the bank's legal director, are suspected of crimes that include facilitating theft, breach of duties, embezzlement and money laundering, authorities said.
The 3.3 billion colones ($6.2 million) in question were first detected missing at the National Bank of Costa Rica in August through internal audits, and last month the attorney general's office announced an investigation.
The principal suspect is a low-level bank employee accused of robbing cash and stashing it away in paper bags out of sight from security cameras, investigators said.
Authorities believe the employee gambled away part of the money.
"I must admit that it hurts me, saddens me and outrages me," the bank's Chief Executive Bernardo Alfaro, said in a video shared by the bank on social media last week.
"The bank will not rest until the investigation reaches its final consequences," said Alfaro, who is also in the running to lead the Central American Bank for Economic Integration.
Attorney General Carlo Diaz said the government was investigating the possibility that orders came from above to not report the theft.
Last week, President Rodrigo Chaves ordered the bank's board of directors be investigated for the handling of the case.
"One is stunned that something like this happens in the country. This seems like something out of a movie (...) This is not a robbery from the National Bank, it is a robbery from Costa Ricans."
($1 = 528.8750 colones)
(Reporting by Alvaro Murillo; Writing by Brendan O'Boyle; Editing by David Gregorio)
By Alvaro Murillo
