Definition: In this task, you need to generate an appropriate title for the given summary of some paragraph. The generated title must be short and should include the main topic of the given text. Your summary should be less than 20 words long.
Input: There is no mystery about who carried out the Paris attacks last week. The two Kouachi brothers and Amedy Coulibaly boasted publicly about their murderous actions before being shot dead by police on Friday. But the question of who was really behind them, if anyone, is triggering a lot of head-scratching from Washington to Paris to Yemen.

Paris attacks: Were gunmen aided by terror network?