According to chamber prosecutor Ove Lundgren, the Swedish Economic Crime Authority (Ekobrottsmyndigheten) estimates the case involves at least 120 million kronor ($16.89 million).
"It involved that much money," he told news agency TT on Tuesday.
Lundgren declined to comment on what the suspects have done or what specific charges he plans to file. According to information from earlier this year, it may involve VAT fraud.
The 42-year-old administrator at the agency has been arrested on suspicion of aggravated fraud and serious breach of trust.
Two other men aged 35 and 37 were detained for aggravated fraud. A fourth person is a suspect in the scandal, but is not currently in custody.
At the end of last year, the agency discovered the scandal when someone responded to a suspicious transaction. When the agency went into its system, it found more suspicious transactions.
In January, an administrator at the agency was reported to the police and later arrested. Two other men were charged in absentia on suspicion of aggravated fraud.
Both have since surrendered and are currently in custody.