Mr Mamu was earlier arrested by Interpol in Egypt on his way to lesser Hajj in Saudi Arabia and was forced to return home to face further questioning by the Nigerian authorities.
Nigeria’s secret police, the State Security Service (SSS), has said it has recovered military uniforms and a large amount of cash in the home and office of Tukur Mamu.
The recovery follows his arrest at the Aminu Kano International Airport on Wednesday.
Mr Mamu, a newspaper publisher, negotiated the release of some of the hostages in the March 2022 train abduction in Kaduna.
Mr Mamu was earlier arrested by Interpol in Egypt on his way to lesser Hajj in Saudi Arabia. He was forced to return home to face further questioning by the Nigerian authorities.
The SSS, in a statement by its spokesperson, Peter Afunanya, said the incriminating items were found after its men conducted a search of the publisher’s properties.
“So far, appropriate security agencies have executed valid search warrants on Mamu’s residence and office.
“During the processes, incriminating materials including military accoutrements were recovered.
“Other items include large amounts in different currencies and denominations as well as financial transaction instruments. While further investigations continue, Mamu will, sure, have a day in court,” he said.
Mr Mamu had, several weeks ago, withdrawn as the lead negotiator in securing the release of the hostages of the Kaduna train abduction. He accused the Nigerian government of threatening his life.
The terrorists who carried out the train attack in March are still holding on to some of the passengers.