A Mexican civilian court has freed the last three soldiers accused of homicide in a 2014 incident in which at least a dozen suspects were allegedly executed after they surrendered.

The federal Attorney General's Office emailed a news release shortly after 11 p.m. Friday saying the court absolved all three of charges of homicide, cover-up and alteration of evidence for lack of proof.

Santiago Aguirre, deputy director of the nonprofit Miguel Agustin Pro Juarez Center for Human Rights, which is representing a woman who survived the incident but whose daughter was killed, said authorities cannot appeal the ruling but families of the victims may still do so.

If there is no appeal, the decision could signal an end to a case that rights groups see as emblematic of abuses by some agents in the Mexican security forces.

"This confirms what we had been warning, in the sense that one of the most serious recent cases of human rights violations was on the way to going unpunished," Aguirre said.

The Mexican army reported in June 2014 that 22 presumed criminals had died in a clash with troops at a warehouse in the town of Tlatlaya west of Mexico City. It said only one soldier was wounded.