A motive has not been identified in the massacre that killed 15 people. (Creative Commons)

Thirteen of the victims worked at the carwash and were clients of Alcance Victoria (Victory Outreach), a drug treatment center. The 14th victim was found dead at a nearby fruit stand, and the 15th victim was shot after arrivign at the carwash.

A witness said the attackers arrived in two SUVs, opening fire first inside the carwash before shooting the workers and manager.

This is the third massacre in Mexico in less than a week. On Sunday, 13 men were kiled in Tijuana at a private drug treatment center. Fourteen were killed just two days before that when gunmen began shooting at a birthday party in Ciudad Juarez.

Officials did not give a motive for Wednesday's shooting.

Read more from the Los Angeles Times here.