A group of protesters was exposing various disagreements when unidentified men opened fire.
Mexican criminal gangs used to avoid targeting the family members of their rivals. But in recent weeks, gunmen have mowed down fathers, mothers and children indiscriminately.
John Blaine Reed, 53, was arrested Thursday by Mexican authorities in the Mexican state of Sonora.
The killings took place Thursday night in the remote hamlet of San José el Mirador, in the municipality of Coxcatlán in the central state of Puebla.
The weekend killings in the Apodaca suburb of the northern city of Monterrey shocked area residents.
U.S. Authorities say the two brothers wanted in the disappearance and presumed slayings of a Washington state couple may be heading for the Mexican border.
Joselo Lucero, whose brother was killed in the 2008 attack, says Patchogue is the wrong place for Trump to visit. "My community has suffered so much discrimination."
The announcement by Miguel Agustín Pro Juárez Human Rights Center and others is the latest step backward in accountability for alleged military killings and rights abuses in the country.
Calling for information, they issued a photograph of a man, dressed in a white shirt and jacket and wearing a dark hat as he pushed a luggage trolley through the airport.
Records showed he stopped attending high school, and family members said he disliked living in the U.S. after moving from Mexico.