Sahel Kazemi

The guy who allegedly sold the gun that killed Steve McNair -- a man named Adrian J. Gilliam Jr. (left) -- has been arrested by ATF agents in Nashville, Tenn. McNair's mistress, Sahel Kazemi, bought the gun on July 2 -- two days before she murdered Steve and then killed herself. Prosecutors are…

TMZ has obtained photos of Steve McNair and Sahel Kazemi on vacation together about three months ago. In the photos, McNair and Kazemi can be seen parasailing together on some kind of beach getaway. It's clear the two had some sort of special relationship. McNair and Kazemi were both found shot to…