An Israeli group campaigning for the release of captives held in Gaza called on Monday for an investigation into the alleged leak of confidential documents by an ex-aide to the prime minister, which may have undermined efforts to secure the captives’ release. An Israeli court announced on Sunday that Eliezer Feldstein, a former aide to Benjamin Netanyahu, had been detained along with three others for allegedly leaking documents to foreign media. The case has prompted the opposition to question whether Netanyahu was involved in the leak. “The families demand an investigation against all those s…