"However, I took one unique aspect of this case into consideration, and as a result, concluded that it is valid not only in the city of Marawi, but in the entire province of Lanao del Sur of which Marawi is a part, and in the provinces of Maguindanao and Sulu as well," she stated in her dissenting opinion.
She also denounced the majority's decision of the Supreme Court and said, "effectively gave Duterte carte blanche"
"... the Court should still have undertaken a factual review of the coverage of martial law. Instead, in refusing to make such effort, the majority has effectively given a carte blanche to the President to exclusively determine this matter," she stated.
"Validating a Mindanao-wide coverage is indeed convenient for the Court but it is not right. If, to use the words of the ponencia, the most important objective of Article VII, Section 18 is to 'curtail the extent of the power of the President,' then this Court miserably failed," Sereno added.
Chief Justice Sereno said that basing from the private briefing provided by Defense Secretary Delfin Lorenzana and Armed Forces chief General Eduardo Año, the atrocities in Mindanao "may have been committed by the Moro National Liberation Front (MNLF), Moro Islamic Liberation Front (MILF), or the New People's Army (NPA)."
"Unless the President is saying that the publicly-announced peace negotiations being conducted with the MNLF, the MILF and the NPA/NDF are being completely abandoned, acts attributable to these 3 rebel groups cannot serve as the factual basis for Proclamation No. 216," Sereno said.
She also said that President Duterte should not use martial law to solve all social ills. Sereno added that Duterte and his administration must not use his authority and power in any way he desires.
"These standards ensure that Marcosian martial law does not happen again and the foundations of a just and humane society envisioned by the Constitution remain intact," Sereno said.
In his part, Senior Associate Justice Antonio Carpio also commented to take President Rodrigo Duterte's words seriously, when he said that his version of martial law "will not be any different from what Marcos did".
"It is apparent that President Duterte does not understand, or refuses to understand, this fundamental principle that forms part of the bedrock of our democracy under the 1987 Constitution, despite his having taking a solemn oath of office to preserve and defend the Constitution," Senior Associate Justice Antonio Carpio in a separate opinion.
Source: Rappler, Sereno's Dissenting Opinion