NEW : Israeli network says 'Prisoner X ' shared Israeli secrets with Israel . The man died in an Australian cell in the previous day ; details have not been released . Israeli lawmakers say they 're investigating the case . Ben Zygier warns against `` overexposure '' of intelligence work .
NEW : Australian network says 'Prisoner X ' shared Israeli secrets with Australia . The man died in an Israeli cell in December 2010 ; details have not been released . Israeli lawmakers say they 're investigating the case . Netanyahu warns against `` overexposure '' of intelligence work .