Working in usurious banks

A: If the reality is as you have mentioned, that, at the time when your brother wrote the check, he did not know that Riba was involved, he will not be blamed for it. He will not be included in the warning that was mentioned in the Hadith that curses those who accept, receive, write, and witness Riba. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.