I insisted that the thief--to be put

翻译为：我坚持认为刚才提及的那个小偷应被投入监狱.（坚持的是被投入监狱）
完整句子：I insisted that the thief who was referred to should be put into prison.
你给的句子省略了两处：the theif （who was）这样reffered to是thief的后置定语
insist翻译为“坚持”接从句要虚拟,用should do或should省略,这里是后者.