MEXICO CITY—Mexico’s president said Thursday he will issue a decree that could release hundreds or thousands of elderly inmates or those who have spent ten years or more in prison and have not been convicted of any violent offense. Anyone who can demonstrate that they suffered torture after they were arrested would also be freed. The move by President Andrés Manuel López Obrador is meant to address the slow, antiquated, and abuse-ridden legal system in Mexico. An estimated 7,200 suspects are in prison on federal charges but with no verdict. It was not clear how many of them have spent a decade behind bars. And because some of them are accused of violent crimes, not all would be released by the Sept. 15 deadline, the president announced. The government has not yet estimated how many will be freed under the decree in total. “The legal framework stipulates that justice has …