Per Pro Football Weekly:
That would seem to fly in the face of all Shawne has said in the past about his Performance Enhancing Drug suspension of 2006. There has been plenty of speculation, most of it by opposing team fans, that Merriman's success in the league (and in the weight room) has been assisted by steroids and this seems to confirm that.
An alternate theory would be that Shawne, after struggling to perform at the same level he did early in his career, has turned to steroids as a way to try and get back to the player he once was.
A third theory would be that Merriman was just holding the steroids for a friend, which is the defense I went with when my mom found cigarettes in my desk when I was 17. That didn't work with her and I doubt it'll go over too well with the NFL either. Now that this news has been released, it will be investigated by the NFL and the Bills OLB could find himself sidelined for much longer than his previous 4-game suspension.
Update from Buffalo Sports Daily:
According to a reliable source close to the situation, Buffalo Bills linebacker Shawne Merriman was caught carrying steroids near the United States border late Thursday night, July 28 on the eve of Bills’ training camp.
According to the source, while trying to cross Canada back into the United States, Merriman was detained by United States Customs shortly after 2:00am. There, the source tells me steroids were found in his possession. He was not arrested and booked because from what I’m told, simply being in the possession of the substance is not technically illegal.
Sounds like Shawne may have been buying the drugs in Canada. I would also like to inform all of the people in prison for possession of a narcotic that they're free to go. Yay!
Update from Shawne Merriman's Twitter:
Absolutely NO steroids found in my vehicle & there were NO charges against me. I've received a great welcome by the community and fans. I've worked my butt off to have a great season.