I thaught mitigation meant reasons to be more lenient and mititation meant reasons to be more severe?
For example "The man would have just been fined for theft but mititating circimstances were found. He was a police officer and should have known better."
Exacerbation or aggravation are opposites for mitigation, both meaning 'making worse'. In the example you give, the fact that the culprit was a policeman made the crime worse.