BAUCHI, Nigeria—Gunmen killed a police officer and abducted five teachers and an unknown number of students on Thursday from a school in the northwestern Nigerian state of Kebbi, police and local residents said. The attack was the latest in a series of group kidnappings at schools in northwest Nigeria, which have been attributed by the authorities to armed bandits seeking ransom payments. A spokesman for the police in Kebbi State, Nafiu Abubakar, said one officer had been shot dead during an exchange of fire between police and gunmen, and a student had also been shot and was receiving medical treatment. “We are still trying to ascertain the number of students kidnapped but five teachers were kidnapped,” Abubakar said. The attack took place at a federal government college in the remote town of Birnin Yauri. Abubakar said security forces were searching a nearby forest for the abducted students and teachers. Atiku …