LAGOS, Nigeria (AP) — Nigeria's Islamic extremists are claiming responsibility for the massive explosion at a busy bus station that killed at least 75 people in Nigeria's capital, Abuja, this week. It comes in a new video received Saturday. The leader of the Boko Haram network threatens more attacks saying "We are in your city, but you don't know where we are." Abubakar Shekau makes no mention of the abductions of more than 100 girls and young women from a remote northeastern school.