Investigators in Matamoros, which borders on Brownsville, Texas, worked to identify the bodies, telling relatives showing up in search of their loved ones that there would be no information until Monday.
Authorities would not release information about the conditions of the bodies or causes of death until the investigation is completed, Tamaulipas state Interior Secretary Morelos Canseco said Saturday.
Families and state governments from around Mexico were calling Tamaulipas on Friday with reports of residents missing from buses that passed through the violent state, where the Gulf and Zetas drug cartels are warring for transport routes to the U.S.
"The state attorney general didn't receive any criminal complaint from any passenger bus line," Canseco said.
Canseco said state and federal officials would work with the companies to beef up security.
Attempts by The Associated Press to get comment from the bus companies Saturday were unsuccessful.
Meanwhile, U.S. officials warned Americans about the dangers of inter-city bus travel in Tamaulipas. The U.S. Consulate General in Matamoros said that between late March and early April it received three reports from U.S. citizens or their families of buses being boarded by criminals.
The consulate warning Friday was the third one about highway travel in Tamaulipas in the past five months.
Investigators uncovered the 72 bodies near San Fernando, a town about 90 miles south of Brownsville on a well-traveled stretch of highway patrolled by the Mexican military that runs near the Gulf Coast.
The same number of migrants were found massacred there last August.
Federal authorities said they are holding 14 people - 12 men and two women - as suspects in the state's second mass killing in less than a year.
The federal Attorney General's Office said there was evidence that most of the suspects belonged to the Zetas drug gang, the same group blamed for the August massacre. Some were detained with military-style uniforms, and others were found driving a pickup truck with false Mexican navy insignia.