Your first main target in Assassin's Creed is Tamir the Black Market Merchant. This is a really easy assassination. If you still need your "Blade in the Crowd" achievement just select your Hidden Blade, walk up behind him and press the X button (Square on PlayStation 3). If you've already done it that way and want to try a fancy pants assassination, then this guide is for you! Remember that this happens in Memory Block 2 so you won't have Throwing Knives or the Counter ability during the investigation.