Monterrey, Mexico (CNN) -- Mexican authorities are asking for DNA samples from families of missing persons nationwide in their efforts to identify 49 decapitated bodies, an official said Wednesday.
That will be the only way to identify the victims -- whose killers cut off their heads, hands and feet -- Nuevo Leon state security spokesman Jorge Domene told reporters three days after investigators found the remains abandoned along a highway.
Officials in El Salvador may also request access to the DNA data authorities in Nuevo Leon have compiled, to compare it with samples from family members of Salvadoran migrants who have gone missing in Mexico, Domene said.
While investigators work to identify the victims behind closed doors, parts of the case have played out quite publicly.
Banners hanging in locations throughout the country, purportedly from the Zetas, claim that the notoriously ruthless cartel had nothing to do with the gruesome crime.
But another message purportedly signed by the Zetas and found Sunday at the crime scene -- a roadside near the industrial city of Monterrey and about 80 miles southwest of the U.S. border -- told a different story, threatening members of rival cartels and Mexican authorities.
Domene told reporters Wednesday that investigations to find those responsible would focus on scientific proof and not on the banners.
On Monday, Mexico's interior minister said the 49 decapitated bodies were likely the result of a fierce feud over territory and power between the Zetas and members of the allied Gulf and Sinaloa cartels.
The Zetas started with deserters from the Mexican army and quickly gained a reputation for ruthless violence as the armed branch of Mexico's Gulf cartel. The partnership ended in 2010.
Now, analysts say the Gulf cartel is allied with the Sinaloa cartel, one of the nation's most powerful drug-trafficking groups.
Interior Minister Alejandro Poire stressed Monday that the Mexican government would not retreat from its efforts to crack down on organized crime -- an effort that is facing increasing criticism as Mexico's presidential campaign season heats up.
"I know very well that these acts worry society, but the solution is not to let our guard down," Poire said.
President Felipe Calderon, seen as the chief champion of Mexico's crime-fighting strategy, is not running for re-election. But opposition candidates have criticized his administration's approach.
More than 47,500 people have died in drug-related violence in Mexico since December 2006, when Calderon announced plans to deploy troops in efforts to combat cartels.
According to Mexico's National Human Rights Commission, more than 5,300 people have disappeared throughout the country in that same time period. And the bodies of 9,000 dead have not been identified.
Officials fear the total number of missing could be far higher, because many disappearances go unreported.
CNNMexico.com contributed to this report.