Who shoots?

[Tom Cook]

This play was described to me last night. Blue 1 fouls and the foul is administered. Play is resumed for 3 or 4 posessions, and Blue 1 is fouled, resulting in free throws. The scorer called the referee over to the bench and informed the officials that Blue 1 had commited his 5th foul on the earlier play. The question is who shoots the free throws? The officials in this game had the substitute shoot them, which I believe is correct, but where is it covered in the rule book? Help will be appreciated!