You are skilled in lining up accurate, deadly shots with your crossbow. Perhaps you add custom-made sights to your weapon, or you have learned to maximize the stability and precision the weapon offers.
Prerequisites: Proficiency and Weapon Focus with hand, heavy, or light crossbow; base attack bonus +1.
Benefit: When using a crossbow for which you have the Weapon Focus feat, you gain a bonus on damage rolls equal to ½ your Dexterity bonus.
If you have the skirmish or sneak attack ability, the maximum range at which you can make such attacks increases to 60 feet when you are using a crossbow for which you have the Weapon Focus feat.
Special: A fighter can select Crossbow Sniper as one of his fighter bonus feats.
Source: Player’s Handbook II, page 77.