"Four out of the five executives were picked up for questioning last night and early this morning," the official said, requesting anonymity due to the continuing investigation.
The four executives were from Oceanic Bank International (Nigeria) Ltd. (NIG.LA), Afribank Nigeria PLC (AFRIBANK.LA), FinBank and Union Bank of Nigeria PLC (UBN.LA).
The managing director of the fifth bank, Intercontinental Bank, isn't in the country and wasn't questioned, according to the official.
"There will definitely be charges against them, and their cronies and accomplices will also be charged," the official said.
The charges that could be filed include fraud, insider trading, share price manipulation, and illegal withdrawal of shareholder funds, among others, according to the official.
The Central Bank injected nearly $2.6 billion into the five banks Friday and ousted their executives after an audit revealed that they were dangerously close to insolvency and laden with bad debts.
Newly installed Central Bank Governor Lamido Sanusi has pledged that no banks will be allowed to fail.
The senior official reinforced this point Tuesday.
"We will go out of our way to make sure the institutions will remain intact," the official said. "But anybody who commits fraud will be jailed."
The ousted managing director of Intercontinental Bank, Erastus Akingbola, was out of the country before the firings last Friday.
"He is out of the country legally, we are waiting for him to come back," the official said. "Whether he wants to come back or not is another question."
Bank spokesmen were unavailable for comment.