A fourth young man also was with the teens and survived the shooting, but now fears for his life and is seeking refuge in the U.S., Gladys Luna, the grandmother of one of the victims, told The Associated Press.
Luna's grandson, 15-year-old Juan Carlos Echeverri was killed Saturday along with 16-year-old Carlos Mario Gonzalez Bermudez and 17-year-old Cesar Yalin Miramontes Jimenez. Echeverri and Gonzalez were U.S. citizens. Miramontes' nationality remains unclear.
Luna said her grandson and three friends had stopped at a dealership Saturday afternoon in one of the world's most dangerous cities, after spotting a car with wheel rims that caught their eye.
"A group of boys or young men, not sure how many, came and asked for the owner of the car dealership," Luna said. "The workers said they didn't know and they started running, hiding."
The group that had asked for the dealership's owner then opened fire at the business that sits not far from the border separating El Paso and Juarez. At least 60 bullet casings were found at the scene.
Luna, who went to Juarez after the shooting Saturday, said she spoke with the survivor, who told her he hid under a car. She said he told her that her grandson was the first one hit by bullets.
"They had nothing to do with this. They had just stopped there to look at cars," Luna said.
Prosecutors in Chihuahua state said they did not know of any survivors from the shooting. Luna said the fourth young man, who currently lives in Juarez, has stayed in hiding and hopes to seek refuge in the U.S.
A friend of the other two victims, El Paso high school student Arturo Yanar, said he had crossed the border to attend a house party with Gonzalez and Miramontes on Friday night.
Yanar said he decided to return home to Texas after the party early Saturday, while his friends stayed on to look at cars. He said Gonzalez had been talking about buying himself a car for months.
"It was a fun night, a great night. At least we had fun one last time together," Yanar said, sniffling.
Yanar is a 16-year-old sophomore at Cathedral High School in El Paso where Gonzalez also was also a sophomore. Echeverri had been a freshman at the same high school last year.
Echeverri, his mother and younger sister had been living with Luna in El Paso. Luna said Echeverri's father had been deported to Mexico recently worked in Spain - and even tried to move the family there to escape the violence in Juarez.
She said Echeverri's father was visiting Juarez until Feb. 15 and that his son had crossed the border to spend time with him.
Reached in Juarez, Echeverri's father, Juan Carlos Echeverri Luna, also told the AP his son and the two others were killed by gunmen looking for someone else, but did not have further details.
Juarez is the center of a fierce turf war between the Sinaloa and Juarez drug cartels. More than 3,000 people were killed last year in the city of 1.3 million residents.
Many Juarez residents travel across the border daily for work or study in El Paso. Some Mexicans live in Texas for safety reasons and commute to Juarez.
Yanar said he grew up in Juarez but had moved to El Paso 18 months ago. He said his father had forbidden him from returning there but that he violated the order go to the party with his friends.
"It just gets worse there and I'm scared," he said of Juarez. "When I walk around, I look back, I look sideways. I always think there's someone following me."
Yanar and another friend, Javier Martinez, 17, said Gonzalez and Miramontes had no problems with gangs or drugs and that they were just in the wrong place at the wrong time.
"He was very brave, he had a lot of courage," Martinez said of Gonzalez, fighting back tears.
Cathedral Principal Nick Gonzalez said 20 to 30 percent of the school's 485 students regularly cross between El Paso and Juarez.
"I was afraid but at the same time resigned that something like this was going to happen," he said. "No one here is shocked, I don't think."
The principal said his students still love the city and "haven't given up on Juarez, or on their lives there."
"That's why, despite the parental warnings, they go," he said. "It's their identity, it's who they are."
After leaving Cathedral, Echeverri was a student at the Radford School in El Paso, enrolling last fall as a sophomore, principal John Doran said.
Doran said Echeverri was the first boy at the private school of 165 students to be killed in Juarez.
"This is a small school, so everybody knows everybody," Doran said. "This is just very hard."
Associated Press writers Juan A. Lozano in Houston, Danny Robbins in Dallas and Olivia Torres in Ciudad Juarez, Mexico, contributed to this report.