Hours after walking out of a federal prison following the dropping of drug trafficking charges against him, a Mexican college student on Friday called on the government to presume the innocence of arrested people rather than require them to prove it.

Oscar Alvaro Montes de Oca was arrested by airport police in Mexico City last week as he returned from Argentina. Authorities asserted he was the owner of a suitcase containing 20 kilograms of cocaine.

He spent a week in custody until authorities relented after the Colombian airline Avianca produced evidence showing the suitcase did not belong to Montes de Oca.

The social sciences student, who appeared at a news conference with the shaved head of a prisoner, thanked everyone who stood by him and fought for his release, especially his school, the Autonomous University of Mexico state.

"I cannot explain the hell I lived," Montes de Oca said. "Unfortunately the state, the current system, makes us all presumed guilty before we're presumed innocent. "

The rector of the university, Jorge Olvera García, who was also at the news conference, noted such cases have happened before in Mexico.

"Justice authorities should call us and we can offer them our services to establish a norm that avoids that this situation happens again," Olvera Garcia said.

On July 13, 2013, Angel de Maria Soto returned to Mexico from Peru and 10 kilograms of cocaine were found in her suitcase. She was released a short time later.

In November of that year, authorities found 27 kilograms of cocaine in a suitcase that carried Ernesto De la Torre Carvajal's bag tag, but the luggage was shown to not be is.

"They manipulated the luggage, changed the tags," De la Torre said after his release.

Montes de Oca said authorities and airlines must come up with a better system than one that allows easily switched tags to be the basis for charging someone with drug trafficking.