Appointment of Inspector-General and control of Nigeria Police Force
Section 215(1)(a) · 1999 Constitution (2004 edition)
What Constitution says
(a) an Inspector-General of Police who, subject to section 216(2) of this Constitution shall be appointed by the President on the advice of the Nigeria Police Council from among serving members of the Nigeria Police Force;
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 96. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections