Mexico's government announced a $110,000 reward for information on the disappearance of 43 students in a case of alleged collusion between a drug gang and police.
The reward was announced in national newspapers and featured black and white photos of the 43 students, who went missing three weeks ago in the southern city of Iguala.
The reward applies to information on the whereabouts of the students or for the identification of those responsible for their disappearance.
Meanwhile, representatives of the students' families expressed wariness over the government's probe of the case. The disappearances have triggered an uproar in this country painfully used to drug-related violence.
The representatives raised their concerns after meeting with Interior Minister Miguel Angel Osorio Chong and Attorney General Jesus Murillo Karam.
"We do not believe in the results (of the investigation) so far because there is nothing that takes us close to the truth," said Felipe de la Cruz, a relative of one of the missing.
"Today we tried to trust the federal government but the results do not satisfy us," de la Cruz said.
Authorities say Iguala's police force shot at buses carrying the students on September 26 and handed them over to officers in the neighboring town of Cocula, who then delivered them to the Guerreros Unidos drug gang.
A total of 36 municipal officers in Iguala have been arrested in the case, along with 17 Guerreros Unidos members and their boss.
The attorney general has said investigators are still analyzing the contents of three mass graves found near Iguala after declaring last week that 28 bodies found in one pit did not belong to the students.