Updated

Three teenage boys were shot to death in the Mexican border city of Ciudad Juarez over the weekend, at least two of them U.S. citizens and high school students in Texas, authorities said.

The boys were killed at 4:22 p.m. Saturday while looking at cars in a dealership in the city across the border from El Paso, Texas, Chihuahua prosecutors' spokesman Arturo Sandoval said. One was found inside a white Jeep Cherokee and the other two in the courtyard.

There were no leads on suspects or a motive, Sandoval said. Two managers were also in the dealership during the attack. One refused to give a statement, while the statement from the other manager was not released because of the pending investigation, Sandoval added. At least 60 bullet casings were found at the scene.

One of the boys, Carlos Mario Gonzalez Bermudez, 16, was a sophomore at Cathedral High School in El Paso, said Nick Gonzalez, the Roman Catholic brother who is the principal. Another victim, Juan Carlos Echeverri, 15, had been a freshman at the private all-boys Catholic school last year, but left to study in Ciudad Juarez, Gonzalez said.

"They were very normal boys," Gonzalez said Tuesday in an interview with Fox News.

Gonzalez confirmed that both Bermudez and Echeverri were U.S. citizens. The nationality of the third victim, 17-year-old Cesar Yalin Miramontes Jimenez, was unclear.

A friend of two of the three teens said the pair had crossed the border from Texas for a party and then stayed to buy a car.

According to the grandmother of Echeverri -- Gladys Luna -- a fourth teen was caught in the shooting and survived, although he is now seeking refuge in America. Luna said the teen told her how the event unfolded.

"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 then opened fire while the fourth teen hid under a car.

The school principal said Gonzalez Bermudez mainly lived in Ciudad Juarez and commuted each day across the border. He said 20 percent of the 485 students enrolled at Cathedral are from Ciudad Juarez.

Gonzalez said the school's sophomore class had a prayer service Monday and officials planned a rosary service for the entire school later in the week.

"It's a lot of pain, a lot of sorrow, a lot of tears, a lot of coming together as a community to try to hold each other up and to try and make sense today," Gonzalez said. "How do you make sense of this meaningless tragedy?"

Gonzalez continued: "Hopefully this can really empower us to make a positive change in the border community because their deaths will have no meaning otherwise."

Many Ciudad Juarez residents travel across the border on a daily basis for work or study. Some Mexicans live in El Paso for safety reasons and commute to Ciudad Juarez.

Ciudad Juarez city has become one of the world's most dangerous cities amid a fierce turf war between the rival Sinaloa and Juarez drug cartels. More than 3,000 people were killed last year in the city of 1.3 million residents.

Gonzalez said students at the school have had a number of relatives killed in the violence in Ciudad Juarez. A graduate of the school was killed last fall, he said.

"Our Juarez kids knew all three" of the teenagers killed over the weekend, he said. "It's a very tight knit community. A lot of them car pool; that's how they know each other."

The three teenagers were killed in one of three triple homicides in Ciudad Juarez over the weekend, the El Paso Times reports.

A teenager, a woman, and a 40-year-old man were killed in a separate shooting attack, according to the newspaper, and another triple homicide left a 13-year-old boy dead.

Click here to read more on the shooting in Ciudad Juarez from the El Paso Times

The Associated Press contributed to this report.