Is he supposed to be omniscient?

Spoilers:

The reveal at the end of episode 12 doesn't seem to make any sense with how little Alex has discussed Andrea (and only with those closest to her). Wasn't she completely off the grid while living with him? It seems that this level of information about someone's brief relationship would be almost impossible to find retroactively since Devlin and the task force were not on each other's radars until recently.