Federal police seized Jose Luis Abarca and his wife, Maria de los Angeles Pineda, in a raid before dawn in Iztapalapa, a working-class neighborhood of the capital. It was a far fall from their reign of wealth and power as the mayor and first lady of Iguala, a town in southern Guerrero state where the students from a teachers college went missing Sept. 26, allegedly at the hands of police and a drug cartel.

Even as they were hauled off to the attorney general’s organized crime unit to give their statements, the capture did nothing to answer the biggest mystery: Where are the students? Their disappearance, and the failure to make progress in the case, has ignited protests across the country and broadsided President Enrique Pena Nieto’s efforts to paint violence in Mexico as a thing of the past.

“News like this just makes you angrier,” said Mario Cesar Gonzalez, whose son, Cesar Manuel Gonzalez, is among the missing. “I wish they would put the same intelligence services and effort into finding the students. The ineptitude is staggering.”

Authorities have uncovered mass graves and the remains of 38 people, but none has been identified as the missing students. Besides Tuesday’s arrests, at least 56 other people have been taken into custody, and the Iguala police chief is being sought.

Some hoped the couple’s detention would provide new leads.

“This was the missing piece. This arrest will help us find our kids,” Felipe de la Cruz, the father of one of the missing students, told Milenio television. “It was the government who took our kids.”

No shots were fired in Tuesday’s raid on three houses, including the one in which the couple was hiding, according to a federal official who spoke on condition of anonymity.

The students attended a radical rural teachers college with a history of carrying out protests. They had gained the enmity of Abarca because of a previous demonstration in the town, Murillo Karam said. Abarca believed they planned to disrupt a speech by his wife, who aspired to succeed him as mayor, and ordered police to detain the students after they hijacked four buses to provide transportation to a coming protest.

Three students were shot dead in the confrontation and later three bystanders were killed in a separate attack.

Police then picked up the other students and took them to the nearby town of Cocula, Murillo Karam said. At some point they were loaded aboard a dump truck and taken — apparently still alive — to an area on the outskirts of Iguala where some mass graves have been found, he said.

In statements to the media soon after the disappearance, Abarca maintained that he spent the evening of Sept. 26 dining out, and that he ordered police to leave the students alone.