Suss goes back at least to Edwardian times, as a cockney abbreviation of the word suspicion.

It arose out of the fact that British policemen were allowed to stop and search anyone out on the streets, especially if they were carrying a bag or rucksack, "on suspicion of possibly going equipped for crime". Referred to as "The Suss Law", it was repealed, I think in the 80s (not certain about that), following claims that it was being abused by police targetting ethnic minority groups.

Don T.