Ngozi Olojeme was head of Nigerian Social Insurance Trust Fund (NSITF) and siphoned off this amount from the fund, an official from the national anti-corruption agency EFCC told AFP.
"She is in our custody for an alleged fraud totally USD 48,485,127 belonging to NSITF," he said, and added that the EFCC had also seized 38 properties traced to Olojeme.
"The properties have been placed under an interim forfeiture in line with a court injunction pending further investigation and trial," he said.
Buhari's electoral pledges included a promise to rid Nigeria of endemic corruption which has stunted its growth.
Critics have accused Buhari of a witch-hunt as only members of the opposition have been targeted in the corruption campaign.
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