TIJUANA, Baja California — A U.S. citizen was among six victims gunned down in a mass shooting in Tijuana on August 18, just two days after the victim’s wife and kids crossed into the United States and claimed asylum.

Phillip Norman Caldwell had been living in Tijuana for the past four months with his wife, Dulce Rosario-Rojas, and their three young children.

The family had bounced around between family shelters and rental units in recent months as they waited for Rosario’s number to be called at the border.

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On August 16, the wife and children crossed safely through the San Ysidro Port of Entry and claimed asylum. They were detained for four days by Customs and Border Protection and then paroled into a downtown San Diego family shelter.

During the family’s detention, Caldwell remained in Mexico at the family’s rental house in the Tres de Octubre neighborhood of Tijuana. In the early evening of August 18, gunmen opened fire and killed six people – including Caldwell – inside a neighboring house.

Caldwell’s landlord owned the house where the mass shooting took place, according to family members, and it remained unclear why the 40-year-old American father was inside his landlord’s house.

A total of four people died inside the house and two victims died later in the hospital, according to Tijuana news media reports. The landlord was one of the two victims who died at the hospital, family members said. 

Tijuana news reports indicated the killings may have been a drug-related, revenge killing linked to an earlier murder at Playas de Tijuana that same day. Those reports were not confirmed by Tijuana homicide investigators.

The Tres de Octubre neighborhood is known a high-crime area, the news reports said. Police arrested three suspects in a vehicle blocks away from the murder scene, and recovered a .223 caliber rifle and a .40 caliber handgun, Tijuana officials said during a news conference. Investigators are running ballistic tests on the weapons to determine if they were used in the killings.

Caldwell was disabled since losing his right leg from the knee down in a motorcycle accident four years ago. He was able to walk using a prosthesis.

For now, Rosario and her three children will remain in the downtown San Diego shelter pending her application for green card as well as their ongoing asylum case.

Rosario will have to start over in her green card application process, now, as the widow of a U.S. citizen. The family is receiving legal assistance from Catholic Charities Diocese of San Diego.

The nonprofit’s Director of Immigration Services, Nadine Toppozada, said the legal team was shocked to learn of Caldwell’s murder.

“I was horrified. It’s a situation that no family wants to find themselves in,” Toppozada said.

CBS News 8 first met the Caldwell’s family in April when they were living in a Tijuana Shelter.

The family said they were forced to migrate to Tijuana because they felt unsafe living in their home in Chiapas, Mexico. Toppozada said Caldwell’s death is, sadly, not unique among asylum seekers. “This is an example of something that happens and this is not the first or last time that we will hear of this,” she said.

“He went to Tijuana to protect his U.S. citizen children and lost his life doing that. It’s a horrible situation, very sad and tragic,” Toppozada said.

The victim’s father, William Caldwell, lives in Fresno and is seeking assistance in retrieving his son’s remains from the morgue in Tijuana.

He said he wants to transport his son back to Alabama, where Phillip Caldwell was born and raised.

Catholic Charities of San Diego is accepting donations to assist the family.

In a statement to News 8, a Department of State official said:

"We can confirm the death of a U.S. citizen in Tijuana, Mexico on August 18. We extend our condolences to the family and loved ones. Whenever a U.S. citizen passes away overseas, the Department of State works to provide all appropriate consular assistance to their family. Out of respect for the family at this difficult time, we have no further comment."