 Wall said that the letter was two paragraphs long and said that due to a concussion Brown cannot remember the incident  but if he did do something wrong then he is sorry.
<meaning-changed>  Wall said that the letter was two paragraphs long and said that due to a concussion Brown cannot remember the incident  but if he did do something wrong then he is sorry.
 Wall said that the letter was two paragraphs long and said that due to a concussion Brown cannot remember the incident due to concussion, but if he did do something wrong then he is sorry.