Not sure exactly, but if cops (let's just call them that for simplicity) are going to have to work with an ex-con, especially one who is recently out of jail and on parole, there's going to be at least one of them who is unhappy about it, thinks it's a bad idea, and just flat out doesn't trust the hacker. That's the "antagonist government agent". There should also be a "sympathetic government agent" who thinks that the hacker is the best hope they have of catching the bad guys. This is good for dramatic tension, but also very realistic IMHO. Lose the antagonist and there's no point in making the hacker an ex-con, lose the sympathetic one and he never gets picked to do the job.