QUETTA, Pakistan — Survivors of an overnight attack that killed 61 people at a Pakistani police academy described chaotic scenes of gunfire and explosions, with militants shooting anyone they saw and cadets running for their lives and jumping from windows and rooftops. A Taliban splinter group and an affiliate of the Islamic State group made competing claims of responsibility for the four-hour siege late Monday at the Police Training College on the outskirts of the southwestern city of Quetta. Most of the dead and the 123 wounded were recruits and cadets, said Wasay Khan, a...