User blog comment:Kaloneous/Mass Effect 3 Ending DLC Denied and PAX/@comment-4043223-20120410185235/@comment-4043223-20120411012257

To answer the questions about the letters then this article originally stated it was over 10,000 letters but was amended less then a day later to say several thousand letters. The information (number) was clarified in the comments section by another user who worked in the gaming industry. The whole thing is now a legal matter between EA and the family who sent the letters and is a closed case until however long it takes the American legal system to release info (if at all, I don't know how the legal system works over there).
 * GamesIndustry.biz.

The likelihood that it was EA is in the fact that the organization called allout.org that was supposedly sending the messages (which were actually spambots) has pointed to it being an EA action and not them, even though they support EA and the right of individuals and the promotion of the rights of individuals and publishers to publish their work. They continue to support EA and requested EA look into it the serious breach of using their organization as a source of spamming.
 * Link