In 'Identity Crisis' (Jun-Dec 2004), we learn that Zatanna wiped Batman's memory a while ago.
In 'OMAC Project' (Jun-Nov 2005), we learn that Batman knew what happened and has a satellite set up to monitor the JLA to prevent further incidents like these.
However, it isn't clear how Batman knew this. I know it's never mentioned in the 'Batman' issues of the time (War Games/Under the Hood/War Crimes).
So, my question is: is it ever made clear how Batman came to know this? Did anyone present at the time tell him? Did Wally? Did Batman deduce it for himself?
If there is indeed a canon explanation, please tell me which issues to read to find it.