The four men and five women discovered dangling from the Colosio Bridge in Nuevo Laredo were handcuffed, blindfolded and bore signs of torture.
A banner hanging from the bridge claimed the victims — between the ages of 25 and 30 — had committed an April 24 car bombing outside a police station, Mexican media reported.
Hours later, the 14 headless bodies were found in black bags in a gray van parked near a trade association.
The heads were in three ice chests found three hours later.
Nuevo Laredo, on the Texas border, is the site of a vicious feud between the Zeta and Gulf cartels.
Last month, another 14 bodies were found abandoned outside the mayor’s office.
More than 50,000 people have been killed since the Mexican government began a crackdown on narco-trafficking in 2006.