Tijuana – Two U.S. citizens were shot to death before dawn Monday as they waited in line to cross the border in their car near San Ysidro, the State Attorney General’s Office announced.

Authorities identified the victims as Sergio Salcido Luna, 25, and Kevin Joel Romero, 28, who carried their U.S. passports with them.

The double homicide happened at 2:40 a.m. at 2nd Street and Puente México in the Río zone.

The victims were shot in the head and their car was sprayed with gunfire. They were driving a Mazda B-500 pickup with California license plates 8S78615. Five 9 mm shell casings were found at the crime scene, state authorities said.

Though it bore the earmarks of having been carried out by organized crime, authorities did not give a motive for the attack, nor has anyone been arrested.

Both men had their wallets when they were found.

State authorities have registered five homicides in Tijuana thus far in April; while March had 49 murders, 14 less than during the same month last year.