Central Bank Governor Patrick Njoroge estimates that about 100 million pieces of the old Sh1,000 notes have been returned in exchange for the new generation currency notes.
Mr Njoroge said banks have collected more than 100 million pieces out 217 million pieces that were in circulation when the demonetisation was announced in June.
This means members of the public have less than a month to return the remaining 117 million pieces of old notes lest they become obsolete after the September 30 deadline.
“We expect to collect more notes as the deadline nears because most people like doing things the last minute,” he said.
The CBK governor warned that those holding illicit cash will find it impossible to bring it back into the financial system hence the true picture will only be known on October 1.
“Those notes will be mere papers come October 1. We have enough new notes in circulation,” he added.
Dr Njoroge also revealed that detectives at Directorate of Criminal Investigations (DCI) are probing cases of suspicious cash transactions that have been flagged by banks during the ongoing demonetisation exercise.
He said some of those cases are of people who wanted to change more than Sh5 million to new currency notes.
“We have shared the information we have gathered so far with the DCI for further investigations. Our role as the regulator is to work with the investigating agencies to ensure that we achieve our goal,” Dr Njoroge said.
He noted investigations on people holding illicit money would continue even after the old notes are phased out.