Who's the shooter?

[Sharpshooternes]

A1 fouls B1 in the second half. Coach requests timeout. This foul happened to be the seventh foul putting B in the bonus. Official is reporting the foul then the time out and the players are mostly back to the benches at this time. It is about here that the scorekeeper informs us that it is the 7th foul. We did not mark the shooter. (I understand we blew it by not marking the shooter) but what is the best way to handle this after the fact when you don't really know who the shooter is? We tried waiting to see if someone would line up coming out of the timeout but it was girls ball so of course they had no idea what was going on. We then asked "Who got fouled before the timeout?" and no one really wanted to fess up they ended up choosing someone on their team and we got going. Of course the opposing coach didn't like that much, rightfully so. But I didn't have any way to determine properly who the shooter should be. Anyone have some constructive advice on how to handle this situation aside from knowing the foul count and marking the shooter after every play?