The vehicles, which had Mexico City tags, were left at an intersection in the Vallarta San Jorge section of Guadalajara, the capital of the western Mexican state of Jalisco, the state Attorney General's office said.
Investigators initially said 23 bodies were at the crime scene, but they later found three more inside the vehicles, Jalisco Attorney General Tomas Coronado said.
The crime scene is near a supermarket and the convention center where the Guadalajara International Book Fair is scheduled to begin Saturday.
Police received a call in the early morning hours about the bodies, all of which were "bound and gagged", Jalisco Public Safety Secretary Luis Carlos Najera told Televisa.
The killers left a message inside one of the vehicles, the public safety secretary said, without revealing the contents.
Municipal security cameras are scattered around the area where the bodies were dumped and it is presumed that they captured images of the killers.
Guadalajara hosted the 16th Pan American Games from Oct 14-30 and the Para Pan American Games ended Sunday.
No serious incidents were reported during the sports event, officials said.
Thousands of police officers were deployed during the events and criminals have now returned to "their daily work", Najera said.
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