"Since we consider this an act of terror, Mexican law allows Mexico to participate in the investigation", Ebrard said, adding "this will be the first investigation of this importance in Mexico's history regarding an act of terror against Mexican citizens in USA territory".
At least seven of those 20 murdered in the massacre were Mexican foreign nationals, as are nine of the 26 injured, according to the Mexican government.
In a press conference, Ebrard said that the government of Mexico is looking into the facts about the shooting, and may take legal measures to extradite the shooters and those who provided the weapons. "Mexicans in the United States", Ebrard said (translation via NBC).
USA investigators believe that the shooter posted a lengthy online manifesto where he went on about a perceived "invasion" of Hispanics before targeting the El Paso Walmart.
Authorities searched for any links between the suspect and the material in the document that was posted online, including the writer's expression of concern that an influx of Hispanics into the U.S. will replace ageing white voters, potentially swinging the White House to Democrats.
Mexico on Sunday threatened to take legal action against the United States for failing to protect its citizens after this weekend's mass shooting in the border city of El Paso.
Juan de Dios Velazquez, who was caught in Saturday's shooting at a Walmart store in El Paso, Texas, U.S., is seen in this undated photo provided by his family, in Ciudad Juarez, Mexico August 5, 2019.
Tens of thousands of Mexicans cross the border legally each day to work and shop in the city of 680,000 full-time residents, and El Paso County is more than 80% Latino, according to the latest census data.
Mexico's President had instructed him to make sure the affected families and the Mexican citizens in the USA are protected through "effective, prompt, expeditious and forceful legal actions", the minister added.
"For Mexico this individual is a terrorist", he said.
The shooting happened just six days after the last major outbreak of shootings in a public place-a food festival in California where a teenager killed three people with an assault rifle and wounded a dozen others before taking his own life in a hail of police gunfire.
Another mass shooting took place early Sunday at a bar in Dayton, a city in the state of OH, killing nine people and injuring 26 others.
He said he would ask USA authorities to turn the bodies over to their Mexican families as soon as possible.
President Trump on Monday morning said the shooter's manifesto was "consumed with racist hate".
Mexico's Foreign Minister Marcelo Ebrard met with the families of the Mexican victims on Monday. A 21-year-old white male shooting suspect was taken into custody in the city which sits along the U.S. -Mexico border.