By PAULINA VILLEGAS and ELISABETH MALKIN

COCULA, Mexico — Mexican investigators planted red flags to mark suspected human remains Tuesday as they combed through a garbage-choked ravine in the search for 43 students missing since they were arrested by the police in the southern city of Iguala a month ago.

Yet as the second day of the search outside this forested mountain town closed, there was no sign that the government was any closer to finding the students.

On Monday, Attorney General Jesús Murillo Karam had raised hopes that the dump outside Cocula might hold a clue to the fate of the students, all young men, who the authorities said were handed over to a local drug gang after their arrests.

Four suspected members of the gang, known as Guerreros Unidos, had been arrested and provided information on Monday that led them to Cocula, about 30 minutes from Iguala.

A day later, Mr. Murillo Karam said that it was too early to speculate on what the Cocula dump might hold. “We cannot do anything while we don’t have full and clear evidence of what happened here,” he said on Tuesday.

The arrests bring to 56 the number of people who have been detained over the students’ disappearance on Sept. 26, including police officers from Iguala and Cocula and gang members.

On Tuesday, residents milled around Cocula’s main square, watching police and soldiers drive through. Jorge Luis Mendoza, 25, a farmer, said that the Guerreros Unidos appeared to have control of the region.

“For a year now, violence and crime have really spiked,” he said. “People cannot travel the roads by night because you always see gunmen on the roads, armed people just watching you.”

Still, even in a town that had become inured to kidnappings, “we are not used to the police or narcos killing students,” he said. “That’s just ugly.”

The disappearance has created a political dilemma for President Enrique Peña Nieto, who has sought to play down the issue of drug violence while he tries to focus on the economy.

Yet the search for the students has consumed Mexican public opinion. Their disappearance has set off violent protests in the state of Guerrero, where they were arrested, and demonstrations in much of the country.

The unrest forced the resignation of Guerrero’s governor, Ángel Aguirre, last week. On Tuesday, the government’s security cabinet flew to Acapulco, the state’s largest city, to meet with the interim governor, Rogelio Ortega Martínez, a sociologist and former university administrator with a background in the state’s leftist movements.

Mr. Peña Nieto was scheduled to meet with relatives of the missing students in Mexico City on Wednesday. Although Mexico’s drug war over the past eight years has produced many massacres that have horrified the country, this case has resonated particularly strongly because the investigation has revealed how effectively the gang penetrated the local government.

Mr. Murillo Karam said last week that Guerreros Unidos had infiltrated Iguala’s city hall and that the mayor’s wife, María de los Ángeles Pineda Villa, had been identified as the gang’s main contact.

Both the mayor, José Luis Abarca, and Ms. Pineda Villa are considered fugitives.