SAN CRISTOBAL DE LAS CASAS, Mexico (AP) _ An alleged leader of the Zapatista rebels has been sentenced to 13 years in prison, even though the key witness against him has disappeared.

Javier Elorriaga Berdegue was convicted Thursday by a federal judge in the Chiapas state capital of Tuxtla Gutierrez on charges of conspiracy, rebellion and terrorism.

Prosecutors claim he is Comandante Vicente of the Zapatista National Liberation Army, which launched an insurgency to pressure the government to improve conditions for Indian peasants in Mexico's impoverished south.

Elorriaga has denied involvement with the rebels.

Human rights lawyers criticized the conviction and called into question both the credibility of the Mexican judicial system and the sincerity of the government in peace talks with the rebels.

``It shows it was a political decision to maintain (him) as a prisoner, because the judge did not follow the law,'' said Elorriaga attorney Pilar Noriega, who works with the social services group Coordinating Council of Non-Governmental Organizations for Peace.

``It is a sign that, in reality, the government does not have the will for dialogue.''

Elorriaga, 35, denies that he belongs to the Zapatista Army or participated in the rebels' uprising on Jan. 1, 1994. He has filed an appeal.

Noriega, in a telephone interview from Mexico City, said there had been no evidence offered to prove Elorriaga's alleged connection to the rebels.

Mexican law requires that defendants' accusers appear for cross-examination, but Elorriaga's accuser was Salvador Morales Garibay, an allegedly disgruntled Zapatista leader who disappeared after giving a statement to a Mexico City judge.

Morales failed to show up for six separate hearings, and his whereabouts are unknown.

``We're talking about a ghost, someone who doesn't exist,'' said attorney Marina Patricia Jimenez of the Fray Bartolome de las Casas Human Rights Center in San Cristobal.

Rebel leader Subcommandante Marcos has said Elorriaga was a courier who ferried secret letters between him and President Ernesto Zedillo in an attempt to arrange peace talks.

Also convicted Thursday was Sebastian Entzin Gomez, an 18-year-old Tzeltal Indian, who was sentenced to six years in prison on charges of conspiracy and rebellion.

Noriega said that conviction was based on a supposed confession through an interpreter who did not speak Entzin's language. His accuser also was Morales.

At least 145 people died at the beginning of the rebellion before the government declared a cease-fire. The two sides have been in peace negotiations for a year, but have made little progress.