Commission President Raul Plascencia says the scene of the killings was altered and bodies were moved to mimic a shootout the army's initial account of how the 22 suspected gang members died.
The army's version almost immediately came under question because only one soldier was wounded. The Associated Press found evidence at the scene didn't match a shootout.
A witness later told the AP that only one man died in an initial shootout and all the others were shot after surrendering.