The suspect was found with fresh human hands, intestines and skull exhumed from Ojokoro cemetery in Ikorodu, police said.
Two locally made pistols and one live cartridge concealed in a bag were recovered from the suspect.
The Lagos Ministry of Education on Friday announced the indefinite closure of Dowen College pending the outcome of investigation into the death.
The kidnappers had abducted an eight-year-old not from his parents in July. The child was rescued six days later.
Mr Odumosu warned the concerned Area Commanders to take necessary action on the full compliance with his order.
