video, Shekau said of the girls: We would also give their hands in marriage because they are our slaves. Many will likely end up becoming mothers -- it's a real horror and over the next years we 'll slowly hear the stories of girls few-by-few as they manage to make it out, Zenn told CNN. Shekau's unbending, almost medieval Salafism sees girls and women as servants for whom education is a sin. Women must go and marry, he said in the video statement. You ca n't get them back The location of the abduction and the numbers involved were shrewd choices by Boko Haram. The girls were pulled from their beds at the school, loaded onto buses and trucks and swiftly transported to remote, hilly, forested areas in the northeastern corner of Nigeria. Boko Haram fighters are able to cross the permeable borders with Cameroon and Chad for resupply and to hide out, and U.S. officials believe some of the girls may already have been taken out of Nigeria. Sani said the timing was no accident: the school was full of both Muslim and Christian pupils taking their final exams. They are likely to be in rural, mountainous and forested areas on the move with fighters, with some forced into marriages, he told CNN. Zenn says it will be very tough to get them back. Boko Haram has likely split up or sold the girls into many small groups, and they can be used as human shields in the event of an attack, he