The Department of State Services (DSS) has recovered incriminating materials in the residence of Tukur Mamu.
Mamu is the negotiator between the Nigerian government and terrorists who abducted Abuja-Kaduna train passengers on March 28.
On Thursday, DSS Public Relations Officer, Peter Afunanya said security agencies executed the search warrant.
He listed items found as military accoutrements, large amounts of different currencies and financial transaction instruments.
The spokesperson Afunanya told reporters that Mamu would soon be charged to court.
The DSS took custody of the citizen on Wednesday after he was intercepted in Egypt.
Mamu was held by Nigeria’s foreign partners in Cairo on Tuesday while on his way to Saudi Arabia.
The negotiator is the publisher of Kaduna-based Desert Herald newspaper.