From Diablo Wiki
Crossbows are found in Diablo III. Along with bows, these ranged weapons can be used by all characters, but they're the specialty of the Demon Hunter. There is also a class-specific type of crossbow, the Hand Crossbows that's only for the Demon Hunter's use.
Other higher level bows may also be specialized, but no information about those has yet been released.
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 Crossbow Images
Several crossbows were seen in a Blizzcon 2010 panel.
None of them were named or described in any way, but it's a nice look at the items, at least.
 Demon Hunter Cinematic
Crossbows are "announced" so to speak, by their prominence in the Demon Hunter's cinematic, released at Blizzcon 2010. The character is seen making extensive use of the dual-wielded Hand Crossbows, before switching to a massive, demon skull headed xbow for a dramatic killing blast of Bolo Shot against the last surviving demon.
 Bows and Xbows Concealed
While a short bow was seen to drop in the WWI June 2008 gameplay movie, no other bows were seen in-game until Blizzcon 2010. There were no bows or ranged weapons of any type available in the Blizzcon 2008 and 2009 demos, presumably deactivated from dropping since Blizzard wished to keep the item types out of sight until the Ranger.
At least so it was thought; a bow was sighted in a screenshot from March 2010, but only after the Demon Hunter was revealed at Blizzcon 2010. No special insight was required to notice the bow; it was just in a dark corner of a screenshot and hard to see. Most likely Blizzard didn't notice it either, else they would not have released the shot at a time when the fifth character was still far from being revealed.
 Archer NPCs
Various NPCs have been seen using bows. Several wandering NPC warriors were seen using them in the WWI 2008 gameplay movie. These archers attempted to accompany Deckard Cain and the Barbarian through the dungeon, but were picked off one at a time by various monsters.
Leah is seen holding a bow in town in the Caravan screenshots released in August 2010. It's unknown if she ever accompanies the player into combat, or is just a sort of apprentice Rogue who only holds the bow for status points while in town.
 Archer Monsters
Skeletal Archers are common enemies in Act One screenshots. It's unknown if there are higher level monster archers found later in the game.
 Bow Images
Prior to the Demon Hunter's debut, the only bows were seen being used by NPCs and monsters. A few sample images below.
Skeletal Archer in action.
|Items of Diablo III  Item Basics Normal Items Legendary Armor I Legendary Armor II Legendary Weapons 1h Legendary Weapons 2h Item Sets|
|Item Basics||Item Modifiers||Inventory||Artisans||Merchants||Miscellaneous |
|Armor - Class-Specific||Weapons - Class-Specific||Crafting Items||Other Items |
|| • Blacksmith Plans
|Waist||Wrists & Hands||Legs & Feet||Head |
|| Voodoo Masks - WD|
| Chest Armor
|| Amulets cont.
|| Rings cont.
40) Puzzle Ring
|| Sources - Wiz|
|| Fist Weapons - Monk
|| Mighty Weapons - Barb|
|| Daibos - Monk
|| Bows |
|Item Sets |