SYDNEY—In a dawn raid in June, federal police searched the household of an Australian state opposition lawmaker in Sydney. That exact working day, in connection with the exact investigation, authorities seized the personal computers and telephones of 4 journalists working for Chinese news companies.

China produced particulars of the raids on its journalists final week right after Australia pulled two of its journalists out of China, shedding even more light-weight on the mounting tensions in between Australia and China that led up to the diplomatic standoff above the…