BENGHAZI, Libya — Witnesses and the authorities have called Ahmed Abu Khattala one of the ringleaders of the Sept. 11 attack on the American diplomatic mission here. But just days after President Obama reasserted his vow to bring those responsible to justice, Mr. Abu Khattala spent two leisurely hours on Thursday evening at a crowded luxury hotel, sipping a strawberry frappe on a patio and scoffing at the threats coming from the American and Libyan governments.

Libya’s fledgling national army is a “national chicken,” Mr. Abu Khattala said, using an Arabic rhyme. Asked who should take responsibility for apprehending the mission’s attackers, he smirked at the idea that the weak Libyan government could possibly do it. And he accused the leaders of the United States of “playing with the emotions of the American people” and “using the consulate attack just to gather votes for their elections.”

Mr. Abu Khattala’s defiance — no authority has even questioned him about the attack, he said, and he has no plans to go into hiding — offered insight into the shadowy landscape of the self-formed militias that have come to constitute the only source of social order in Libya since the fall of Col. Muammar el-Qaddafi.

A few, like the militia group Ansar al-Shariah that is linked to Mr. Abu Khattala and that officials in Washington and Tripoli agree was behind the attack, have embraced an extremist ideology hostile to the West and nursed ambitions to extend it over Libya. But also troubling to the United States is the evident tolerance shown by other militias allied with the government, which have so far declined to take any action against suspects in the Benghazi attack.