Same thought I had, not too likely the thief was crediting some random accounts.
This reminded me of a similar situation I ran into with a local credit union. I noted a withdrawal I knew was not mine (by checking my online account access) and called my local branch - and they said yes, it was. When I asked when and where they told me which branch, and I immediately understood what had happened. An individual with same first and last name as myself lives relatively nearby, they apparently had an account with same CU but did banking at a different branch and had made a cash withdrawal. The teller must have not bothered to check account numbers and simply stopped looking when finding a matching name on an account, which happened to be mine.
While on the phone, I stated where I was on that date and time, which was no where near that branch. Could hear some keystrokes being keyed in, followed by a few moments of silence that were quite telling, and then an apology coming from the person on the other end. In the minute or two it took me to log back into my account, all sign of that phantom withdrawal had vanished.