The victims, ages 19 to 23 years old, were found tied up on Saturday, but their deaths were not reported earlier because they were under investigation, said Fermin Gomez, an assistant state prosecutor in Baja California.
U.S. consular officials in Tijuana said the victims -- two men and two women from the San Diego and Chula Vista areas -- were U.S. citizens. The state attorney general's office in Baja California said one of the women was Mexican.
Their deaths are the latest in a string of violence in Tijuana that authorities blame on a bloody turf war between drug cartels.
"I just don't think kids should be going to Tijuana right now," Chula Vista police Lt. Scott Arsenault told the San Diego Union-Tribune. "They ran into the wrong people, obviously."
Bernard Gonzales, a spokesman for the Chula Vista Police Department, said a friend told the women's parents they were headed to nightclubs in Tijuana on Thursday night. They were reported missing the next day when they did not answer their cell phones.
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