Parents of 43 students missing from the Mexican state of Guerrero marched Thursday in Mexico City to mark six months since their children disappeared. The parents dispute the government’s claim local police gave the students to drug gang members, who killed and incinerated them. Epifanio Álvarez, whose son is among the missing, spoke at the march.

Epifanio Álvarez: “For us to believe, they need to give us an answer, and there has been no reply. We are the same as we started. What the government has done is hurt us, the parents, by giving us bad news after bad news, without scientific proof. But we will continue forward. We are united. Years can go by, but we will remain united.”

A number of the students’ parents have come to the United States where they are traveling across the country in three caravans to draw attention to the U.S. role in the drug war.