I have often cited Virginia Comolli, from IISS as a SME on BH and Nigeria. Soon she has a book published, which has excellent reviews:http://www.hurstpublishers.com/book/boko-haram/

Hat tip to save £ or US$ plus. If you register with Hurst for publication notices you can order a book pre-publication, at a reduced price and with free international P&P. This book is £16, not £20.