Joining the dots together, something binary like DUI sounds the most plausible. Timeframe too compressed otherwise, as 99% of other reasons to remove a commander would take a little time to percolate, and ironically, given O'Malleys history, I suspect he might be on the less hasty side when it comes to such a drastic step. An infringement of that nature, involving external authorities would leave him little choice, a judgement which I am sure he would have "road tested" up the line before implementing.