A civilian grand jury is investigating the deaths of two detainees at a U.S. jail in Afghanistan nearly 5 years ago, according to current and former service members who said they’ve testified.

A noon deadline imposed on 21 surviving South Korean hostages kidnapped by the Taliban approached Wednesday with negotiations apparently deadlocked and international concern growing.

Police at daybreak Tuesday discovered the body of a second South Korean hostage slain by the Taliban, officials said. A purported Taliban spokesman had said the hostage was killed because the Afghan government failed to release imprisoned insurgents