CIUDAD JUÁREZ, Mexico  Mayor José Reyes Ferriz is supposed to be the one to hire and fire the police chief in this gritty border city that is at the center of Mexico’s drug war. It turns out, though, that real life in Ciudad Juárez does not follow the municipal code.

It was drug traffickers who decided that Chief Roberto Orduña Cruz, a retired army major who had been on the job since May, should go. To make clear their insistence, they vowed to kill a police officer every 48 hours until he resigned.

They first killed Mr. Orduña’s deputy, Operations Director Sacramento Pérez Serrano, together with three of his men. Then another police officer and a prison guard turned up dead. As the body count grew, Mr. Orduña eventually did as the traffickers had demanded, resigning his post on Feb. 20 and fleeing the city.

Replacing Mr. Orduña will also fall outside the mayor’s purview, although this time the criminals will not have a say. With Ciudad Juárez and the surrounding state of Chihuahua under siege by heavily armed drug lords, the federal government last week ordered the deployment of 5,000 soldiers to take over the Juárez Police Department. With the embattled mayor’s full support, the country’s defense secretary will pick the next chief.