But Mr. Anwar’s detention has not assuaged supporters of the P.T.M. At Sunday’s rally, the first in the city since the killings in January, chants of “Justice for Naqeebullah” soon became calls for “Justice for Pashtuns.”

In the days before the rally, P.T.M. organizers worked in Pashtun neighborhoods across the city to muster grass-roots support for the event. Among a small group of organizers, men mostly in their late 20s and early 30s, all said their childhoods in Pakistan’s tribal areas were marred by violence and chaos as their villages were caught in the crossfire between militants and the military.

“We grew up surrounded by war,” said Kiffayat Ullah, one of the P.T.M.’s core members. “Until this movement, we were too scared to speak up.” Mr. Ullah said that he understood the immense risk involved in challenging Pakistan’s military establishment, but that the P.T.M.’s popular support galvanized him and others. “After Naqeebullah’s death, I know my blood is expensive,” he said.

Much of Karachi’s Pashtun population migrated from the country’s tribal belt, along Pakistan’s border with Afghanistan, after heavy clashes between the state and the Pakistani Taliban, known as the Tehrik-e-Taliban Pakistan or T.T.P. The fighting left their home provinces all but razed. The military warned most civilians to evacuate the areas, forcing many in the local population to flee to urban centers like Karachi.

But the city offered no respite from the war they fled, said Rizwan Mehsud, a young Karachi resident who helped the P.T.M. organize the rally. “When we left the tribal areas, we thought there’d be peace here,” Mr. Mehsud said. “But here, if the police asked to see my ID and saw where I was from, they’d pull me aside for questioning, asking for a bribe to avoid more problems.”

Image Naqeebullah Mehsud, a Pashtun shopkeeper and aspiring model, was killed by the police in Karachi in January. Credit... Family of Naqeebullah Mehsud, via Agence France-Presse — Getty Images

Many of the P.T.M. activists said they had family members who were missing, and they carried posters with photographs of the missing at Sunday’s rally. They believe that the military establishment is to blame. One of the main demands of the rally was the release of missing persons held by the military or information about their whereabouts.