circle that they cannot act with impunity. reporter: speaking to cnn, former uk prime minister gordon brown said that at the request of ukrainian officials, he s lobbying for a special tribunal modeled on the nuremberg trials of nazi criminals and the tribunal investigating atrocities in the former yugoslavia, like the murder of thousands of men and boys in serb neetsia. how can you realistically can you get officials including vladimir putin into a courtroom? they said it was impossible in 1942 when the allies said they were going to try hitler and his accomplices for crimes what we called crimes against peace. but that happened in nuremberg. reporter: a tribunal creates a legal loophole to prosecute putin and senior officials for the act of invading ukraine itself. a crime of aggression. with the right resources, brown says an indictment could come in months.