There is a logical problem with the combination of either 'likely' or 'probable' and 'suspects'. Suspects have, by definition, some likelihood or probability of guilt. That is why they are suspects.
"probables responsables" literally is 'those who are likely/probably responsible for..."
There may be legal jargon that is conventionally, and erroneously, used for this expression that commits the redundancy of combining 'suspects' and an adjective such as likely or probable, but it would be illogical.