Mexican authorities are probing what led gunmen to attack an SUV in Ciudad Juarez, across the border from El Paso, Texas, killing four people, including two U.S. citizens.

Those citizens are Pablo Noe Williams, 19, and his mother, Rosa Williams, 35.

A spokeswoman for the U.S. Consulate in Juarez said officials are working to return their bodies to the U.S.

The others killed were identified as a married couple from Mexico: 24-year-old Alberto Nieto Nieto and 21-year-old Alma Yesenia Flores.

At a special church service honoring Pablo Williams on Wednesday night, Youth Pastor Jimmy De Lao said he was saddened to learn that his friend was killed.

"Our goal tonight is not only to remember Pablo but to celebrate where he's at now,” De Lao said Wednesday. “Because that belief actually represents who we (the youth group) are."

Other friends described Pablo Williams as a quiet man with a strong belief in God.