Those cynical attitudes — rooted in Yemen’s history of manipulative politics — complicate any effort to track down the perpetrators of the recent plot to send explosives by courier to the United States. They also make it harder to win public support for the fight against jihadist violence, whatever label one attaches to it.

“What is Al Qaeda? The truth is there is no Al Qaeda,” said Lutfi Muhammad, a weary-looking unemployed 50-year-old walking through this city’s tumultuous Tahrir Square. Instead, he said, the violence is “because of the regime and the lack of stability and the internal struggles.”

That view, echoed across Yemen, is only partly a conspiracy theory. The Yemeni government has used jihadists as proxy soldiers in the past, and sometimes conflates the Qaeda threat and the unrelated political insurgencies it has fought in northern and southern Yemen in recent years. In a country where political and tribal violence is endemic, it is often impossible to tell who is killing whom, and why.