GUATEMALA CITY - A Guatemalan judge on Tuesday dropped charges against a former prison director accused of participating in the killings of 10 inmates.

Judge Patricia Flores on Tuesday ordered the release of Alejandro Giammattei, who was arrested last summer, saying there was not enough evidence to prosecute him.

A former presidential candidate, Giammattei was among 19 people accused of plotting the killings of seven inmates during a 2007 uprising at Pavon prison and the alleged execution of three inmates who escaped from the "El Infiernito" prison in 2005.

Then-Interior Minister Carlos Vielmann is also charged in the case. Vielmann was arrested in Spain in October 2010, and the extradition request by Guatemala is pending.

The accused also include the former head of the national police, Erwin Sperisen, whose extradition from Switzerland is also pending.

The UN International Commission Against Impunity in Guatemala, established to handle similar cases, accused Giammattei, Vielmann and Sperisen of belonging to a criminal organization that carried out executions.