A federal judge in Mexico has opened a court proceeding against three prison employees on charges they aided in the escape of drug lord Joaquin "El Chapo" Guzman.

In a statement Friday, Federal Judiciary Council said the legal process would advance in the cases of three of the seven originally arrested in relation to Guzman's July 11 escape from a maximum-security prison.

It said prosecutors showed there was sufficient evidence that the employees favored Guzman's escape through a one-mile long tunnel.

It described the employees as the person in charge of the prison's video surveillance control center and two guards. There were inconsistencies in the supervisor's statements and there was no explanation for why the guards did not answer the telephone in their module.