Thousands of protesters blocked the highway leading to Acapulco in southern Mexico on Thursday to press authorities to find 43 students missing since a deadly police shooting last weekend.
The demonstration was part of commemorations of a 1968 massacre of students by the army in Mexico City but the protesters focused on the fate of the disappeared in violence-plagued Guerrero state.
Parents of the missing led the march in the state capital Chilpancingo, holding signs saying "they were taken alive, we want them back."
The students, from a teacher training college near Chilpancingo, had gone to the town of Iguala 100 kilometers (62 miles) to the north last Friday to raise funds when they were shot at by municipal police after they hijacked buses to return home.
Three students were killed and witnesses said they saw dozens taken away in police cars.
Authorities detained 22 officers over the shooting and another attack that killed three other people later that night on the outskirts of Iguala. A gang is suspected of participating in the second shooting and the officers are suspected of having links to criminals in the region, raising fears a gang has the students.
"We are fed up with crime and corruption in this state," said Manuel Martinez, 32, whose 18-year-old nephew is among the missing.
Relatives of the missing, backed by scores of troops and state police, scoured fields and communities around Iguala this week, handing out flyers with pictures of their loved ones.
But the parents said they are unhappy with how authorities are handling the case, saying no proper investigations are being conducted for the search.
"The search was a show," said Mariano Flores Vazquez, 35, who searched for his 22-year-old nephew.
Manuel Olivares, coordinator of the Guerrerense Network of Human Rights Organizations, told AFP the parents are debating how to proceed with the search.
"The parents didn't like how it took place because there's no seriousness, there's no investigation," he said.
Officials say they hope the 43 students will turn up alive like a dozen others who reappeared after apparently going into hiding.
The parents are holding out hope but some fear for the worst in a country where 80,000 people have been killed in drug-related violence since 2006. Another 22,000 people are unaccounted for.