When you say the bank statements are online, do you mean his personal account or is it a joint one? If the latter then, as someone's already pointed out, you can obtain statements from the bank directly. However if the account is in his name only, then you won't find out anything. I suspect the 3k has been withdrawn so he doesn't need to use a debit/credit card for transactions. In other words there will be no trace of what he spends it on - and that is very suspicious.
Please don't hang back for too long.