A judge in Mexico has handed down the first conviction ever of a Mexican soldier for the disappearance of a civilian.

Mexico's Federal Judiciary Council announced the verdict Tuesday. The second lieutenant was sentenced to just over 31 years in prison for illegally detaining and causing the disappearance of the victim in the northern state of Nuevo Leon in 2012.

The victim was not identified, and was never found.

Despite hundreds of complaints, Mexico has had only six convictions of public officials in connection with disappearances.

All of those convicted previously were police agents. The crime is formally known in Mexico as "forced disappearance."

An aggravating factor in the sentencing was the suffering of the victim's family and their battle to find out the truth.