This article from Fox News Latino summarizes the changes made by the decree as follows:
The law, which took effect Saturday [June 14], states that military police will conduct investigations under the direction of civilian prosecutors and be required to offer assistance to victims and protection to witnesses.
They also will be tasked with arresting military suspects and immediately turning them over to civilian prosecutors.
Armed forces members who are accused of crimes against civilians may be held in pre-trial detention in military lockups when military authorities deem it necessary to protect their rights.
In such cases, military authorities will cooperate with the civilian courts to ensure the accused appears before the judicial authorities when summoned.
The law states that crimes committed by an armed forces member against a fellow soldier will be tried in military courts.
It also requires military courts to use the adversarial judicial model being adopted in Mexico to ensure presumption of innocence and protect soldiers' human rights.Other provisions of the decree are summarized here.