The Mexican Attorney General's Office on Monday announced they arrested a person for his alleged involvement in Saturday's attacks which killed 14 people in Reynosa.

Federal investigators said Jonathan "R" was put under federal custody because he had a long firearm that is exclusively used in the armed forces, according to a news release.

In a press conference on Monday morning, Mexican president Andrés Manuel López Obrador said, "It was a cowardly attack that took the lives of innocent people." He sent his condolences to the affected families.

Federal and state investigators continue to investigate Saturday's attacks which led to the death of 14 people and five armed civilians in Reynosa.

Investigators said the motive for Saturday's killings was a result of a turf war between criminal groups in Río Bravo fighting against cartels that operate in Reynosa.

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The federal Attorney General's Office said it began its investigation after the state of Tamaulipas requested they get involved. The state said Saturday's killings also violated federal laws because it involved organized crime and the use of military-grade weapons. State investigators will continue to investigate crimes that may have violated state laws.

Tamaulipas Gov. Francisco García Cabeza de Vaca reacted to the series of deadly shootings, calling the acts "reprehensible" in a news release on Sunday afternoon.

Gov. García Cabeza de Vaca said the victims were innocent and ordered the incidents be investigated a quickly as possible so those responsible could be prosecuted.

"I express my solidarity with the families of the innocent victims that died as a consequence of organized crime in Reynosa," Gov. García Cabeza de Vaca said in a news release.

He called on the federal and state government to assume their responsibility in "the fight against those that threaten the safety, health and stability of the community."

Gov. García Cabeza de Vaca said the state government will provide the assistance necessary to help the families of the victims. The governor added, "organized criminal organizations should receive a clear, direct and explicit message from the federal government that there will be no space for impunity, nor will there be tolerance for their reprehensible criminal actions."

On Sunday, Reynosa mayor Maki Ortiz called the murders "very unfortunate," in an interview with Channel 5's sister-station Azteca Valle.

"We are in touch with the local coroner's office to see if they could provide the families of the victims with help paying for funeral expenses," Ortiz said.

Francisco "Paco" Rojas, a reporter with ReynosaNews.com said, "We unfortunately live in a very volatile area, and yet it's full of military presence from the Navy, Army, state police, state police investigators and the National Guard. And even then Reynosa residents still feel unsafe," Rojas said.

Rojas told Channel 5's sister-station Azteca Valle, eyewitnesses reported seeing a shooting start at a park in the Unidad Obrera neighborhood on the city's east side closest to the Pharr International Bridge.

On Saturday afternoon, a group of young people were at the park playing a soccer game. Rojas said armed civilians began firing weapons towards the group of people.

When authorities arrived, the armed civilians fled and began shooting at people on the street.

--- Enrique Lerma reported for Azteca Valle.

Correction: Fourteen people and five armed civilians were killed on Saturday.