The Department of State Services (DSS) discovered incriminating materials in Tukur Mamu’s home.
Mamu is the mediator between the Nigerian government and the terrorists who kidnapped passengers on the Abuja-Kaduna train on March 28.
According to DSS Public Relations Officer Peter Afunanya, security agencies carried out the search warrant on Thursday.
He described the items discovered as military accoutrements, large amounts of various currencies, and financial transaction instruments.
Afunanya, the spokesperson, told reporters that Mamu would be charged in court soon.
The DSS apprehended the citizen on Wednesday after he was apprehended in Egypt.
On his way to Saudi Arabia, Mamu was detained by Nigeria’s foreign partners in Cairo on Tuesday.
The negotiator is the publisher of the Desert Herald newspaper in Kaduna.
